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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH 1 of 4 v6/leftover] libxl: enable automatic placement of guests on NUMA nodes
If a domain does not have a VCPU affinity, try to pin it automatically
to some PCPUs. This is done taking into account the NUMA characteristics
of the host. In fact, we look for a combination of host's NUMA nodes
with enough free memory and number of PCPUs for the new domain, and pin
it to the VCPUs of those nodes.
Deciding which placement is the best happens by means of some heuristics.
For instance, smaller candidates are better, both from a domain perspective
(less memory spreading among nodes) and from the entire system perspective
(smaller memory fragmentation). In case of candidates of equal sizes
(i.e., with the same number of nodes), the amount of free memory and
the number of domains' vCPUs already pinned to the candidates' nodes are
both considered. Very often, candidates with greater amount of memory
are the one we wants, as this is good for keeping memory fragmentation
under control. However, we do not want to overcommit some node too much,
just because it has a lot of memory, and that's why the number of vCPUs
must be accounted for.
This all happens internally to libxl, and no API for driving the
mechanism is provided for now. This matches what xend already does.
Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Acked-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
Changes from v5:
* macros moved from libxl_numa.c to libxl_internal.h.
* Changed the placement heuristics that now considers how many
vCPUs are already pinned to a candidate, instead of how many
domains, as suggested during testing/review (thanks a lot Andre!).
* Changed the weights in the placement heuristics so that, now,
CPU load counts more than free memory, as suggested during
testing/review (thanks a log again Andre! :-D).
* Removed the separation between generating the list of possible
candidates and sorting that list. Now the best candidate is selected
on-line, without the need of keeping track of more than 2 candidates
at a time.
* Thanks to the above, the placement can now end earlier, i.e., as soon as
a placement is found and all the other candidates with the same number
of nodes have been checked (as bigger candidates would be worse than
that anyway).
* Avoid running any placement if the system has more than 8 nodes,
as agreed during review.
* Avoid running any placement if the config file has a "cpus='all'"
directive, as suggested during review.
Changes from v3:
* fixed a double free on non-NUMA systems (namely, when just 1 node exists).
* Reword an ambiguous sentence in xl's man page, as requested during review.
* Do no special case single node systems in libxl__get_numa_candidates(), to
avoid generating a spurious warning on them.
Changes from v2:
* lots of typos.
* Clayfied some comments, as requested during (ijc's) review.
* Added some more information/reference for the combination generation
algorithm.
* nodemap_to_nodes_cpus() function renamed to nodemap_to_nr_cpus().
* libxl_bitmap_init() used to make sure we do not try to free random
memory on failure paths of functions that allocates a libxl_bitmap.
* Always invoke libxl__sort_numa_candidates(), even if we get there
with just 1 candidate, as requested during review.
* Simplified the if-s that check for input parameter consistency in
libxl__get_numa_candidates() as requested during (gwd's) review.
* Comparison function for candidates changed so that it now provides
total ordering, as requested during review. It is still using FP
arithmetic, though. Also I think that just putting the difference
between the amount of free memory and between the number of assigned
domains of two candidates in a single formula (after normalizing and
weighting them) is both clear and effective enough.
* Function definitions moved to a numa specific source file (libxl_numa.c),
as suggested during review.
Changes from v1:
* This patches incorporates the changes from both "libxl, xl: enable automatic
placement of guests on NUMA nodes" and "libxl, xl: heuristics for reordering
NUMA placement candidates" from v1.
* The logic of the algorithm is basically the same as in v1, but the splitting
of it in the various functions has been completely redesigned from scratch.
* No public API for placement or candidate generation is now exposed,
everything happens within libxl, as agreed during v1 review.
* The relevant documentation have been moved near the actual functions and
features. Also, the amount and (hopefully!) the quality of the documentation
has been improved a lot, as requested.
* All the comments about using the proper libxl facilities and helpers for
allocations, etc., have been considered and applied.
* This patch still bails out from NUMA optimizations if it find out cpupools
are being utilized. It is next patch that makes the two things interact
properly, as suggested during review.
diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -111,8 +111,8 @@ created online and the remainder will be
=item B<cpus="CPU-LIST">
-List of which cpus the guest is allowed to use. Default behavior is
-`all cpus`. A C<CPU-LIST> may be specified as follows:
+List of which cpus the guest is allowed to use. By default xl will pick
+some cpus on its own (see below). A C<CPU-LIST> may be specified as follows:
=over 4
@@ -132,6 +132,12 @@ run on cpu #3 of the host.
=back
+If this option is not specified, libxl automatically tries to place the new
+domain on the host's NUMA nodes (provided the host has more than one NUMA
+node) by pinning it to the cpus of those nodes. A heuristic approach is
+utilized with the goals of maximizing performance for the domain and, at
+the same time, achieving efficient utilization of the host's CPUs and RAM.
+
=item B<cpu_weight=WEIGHT>
A domain with a weight of 512 will get twice as much CPU as a domain
diff --git a/tools/libxl/Makefile b/tools/libxl/Makefile
--- a/tools/libxl/Makefile
+++ b/tools/libxl/Makefile
@@ -66,7 +66,7 @@ LIBXL_LIBS += -lyajl -lm
LIBXL_OBJS = flexarray.o libxl.o libxl_create.o libxl_dm.o libxl_pci.o \
libxl_dom.o libxl_exec.o libxl_xshelp.o libxl_device.o \
libxl_internal.o libxl_utils.o libxl_uuid.o \
- libxl_json.o libxl_aoutils.o \
+ libxl_json.o libxl_aoutils.o libxl_numa.o \
libxl_save_callout.o _libxl_save_msgs_callout.o \
libxl_qmp.o libxl_event.o libxl_fork.o $(LIBXL_OBJS-y)
LIBXL_OBJS += _libxl_types.o libxl_flask.o _libxl_types_internal.o
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -98,6 +98,102 @@ out:
return sched;
}
+/* Subtract two values and translate the result in [0, 1] */
+static double normalized_diff(double a, double b)
+{
+ if (!a && a == b)
+ return 0.0;
+ return (a - b) / MAX(a, b);
+}
+
+/*
+ * Two NUMA placement candidates are compared by means of the following
+ * heuristics:
+
+ * - the amount of free memory and the number of vcpus runnable on the
+ * candidates are considered. In doing that, candidates with greater
+ * amount of free memory and fewer runnable vcpus are preferred. Also,
+ * the difference in number of vcpus "weights" three times as much as
+ * the amount of free memory.
+ *
+ * In fact, leaving larger memory holes, maximizes the probability of being
+ * able to put other domains on the node. That hopefully means many domains
+ * will benefit from local memory accesses, but also introduces the risk of
+ * overloading large (from a memory POV) nodes. That's right the effect
+ * that counting the vcpus able to run on the nodes tries to prevent.
+ *
+ * Note that this completely ignore the number of nodes each candidate span,
+ * as the fact that fewer nodes is better is already accounted for in the
+ * algorithm.
+ */
+static int numa_cmpf(const libxl__numa_candidate *c1,
+ const libxl__numa_candidate *c2)
+{
+ double freememkb_diff = normalized_diff(c2->free_memkb, c1->free_memkb);
+ double nrvcpus_diff = normalized_diff(c1->nr_vcpus, c2->nr_vcpus);
+
+ return SIGN(freememkb_diff + 3*nrvcpus_diff);
+}
+
+/* The actual automatic NUMA placement routine */
+static int numa_place_domain(libxl__gc *gc, libxl_domain_build_info *info)
+{
+ int found;
+ libxl__numa_candidate candidate;
+ libxl_bitmap candidate_nodemap;
+ libxl_cpupoolinfo *pinfo;
+ int nr_pools, rc = 0;
+ uint32_t memkb;
+
+ libxl__numa_candidate_init(&candidate);
+ libxl_bitmap_init(&candidate_nodemap);
+
+ /* First of all, if cpupools are in use, better not to mess with them */
+ pinfo = libxl_list_cpupool(CTX, &nr_pools);
+ if (!pinfo)
+ return ERROR_FAIL;
+ if (nr_pools > 1) {
+ LOG(NOTICE, "Skipping NUMA placement as cpupools are in use");
+ goto out;
+ }
+
+ rc = libxl_domain_need_memory(CTX, info, &memkb);
+ if (rc)
+ goto out;
+ if (libxl_node_bitmap_alloc(CTX, &candidate_nodemap, 0)) {
+ rc = ERROR_FAIL;
+ goto out;
+ }
+
+ /* Find the best candidate with enough free memory and at least
+ * as much pcpus as the domain has vcpus. */
+ rc = libxl__get_numa_candidate(gc, memkb, info->max_vcpus, 0, 0,
+ numa_cmpf, &candidate, &found);
+ if (rc)
+ goto out;
+
+ /* Not even a suitable placement candidate! Let's just don't touch the
+ * domain's info->cpumap. It will have affinity with all nodes/cpus. */
+ if (found == 0)
+ goto out;
+
+ /* Map the candidate's node map to the domain's info->cpumap */
+ libxl__numa_candidate_get_nodemap(gc, &candidate, &candidate_nodemap);
+ rc = libxl_nodemap_to_cpumap(CTX, &candidate_nodemap, &info->cpumap);
+ if (rc)
+ goto out;
+
+ LOG(DETAIL, "NUMA placement candidate with %d nodes, %d cpus and "
+ "%"PRIu32" KB free selected", candidate.nr_nodes,
+ candidate.nr_cpus, candidate.free_memkb / 1024);
+
+ out:
+ libxl__numa_candidate_dispose(&candidate);
+ libxl_bitmap_dispose(&candidate_nodemap);
+ libxl_cpupoolinfo_list_free(pinfo, nr_pools);
+ return rc;
+}
+
int libxl__build_pre(libxl__gc *gc, uint32_t domid,
libxl_domain_build_info *info, libxl__domain_build_state *state)
{
@@ -107,7 +203,22 @@ int libxl__build_pre(libxl__gc *gc, uint
uint32_t rtc_timeoffset;
xc_domain_max_vcpus(ctx->xch, domid, info->max_vcpus);
+
+ /*
+ * Check if the domain has any CPU affinity. If not, try to build up one.
+ * In case numa_place_domain() find at least a suitable candidate, it will
+ * affect info->cpumap accordingly; if it does not, it just leaves it
+ * as it is. This means (unless some weird error manifests) the subsequent
+ * call to libxl_set_vcpuaffinity_all() will do the actual placement,
+ * whatever that turns out to be.
+ */
+ if (libxl_bitmap_is_full(&info->cpumap)) {
+ int rc = numa_place_domain(gc, info);
+ if (rc)
+ return rc;
+ }
libxl_set_vcpuaffinity_all(ctx, domid, info->max_vcpus, &info->cpumap);
+
xc_domain_setmaxmem(ctx->xch, domid, info->target_memkb +
LIBXL_MAXMEM_CONSTANT);
if (info->type == LIBXL_DOMAIN_TYPE_PV)
xc_domain_set_memmap_limit(ctx->xch, domid,
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -2216,6 +2216,125 @@ static inline void libxl__ctx_unlock(lib
#define CTX_LOCK (libxl__ctx_lock(CTX))
#define CTX_UNLOCK (libxl__ctx_unlock(CTX))
+#define SIGN(x) ((x) > 0 ? 1 : (x) < 0 ? -1 : 0)
+#define MAX(x, y) ((x) > (y) ? (x) : (y))
+
+/*
+ * Automatic NUMA placement
+ *
+ * These functions and data structures deal with the initial placement of a
+ * domain onto the host NUMA nodes.
+ *
+ * The key concept here is the one of "NUMA placement candidate", which is
+ * basically a set of nodes whose characteristics have been successfully
+ * checked against some specific requirements. More precisely, a candidate
+ * is the nodemap associated with one of the possible subset of the host
+ * NUMA nodes providing a certain amount of free memory, or a given number
+ * of cpus, or even both (depending in what the caller wants). For
+ * convenience of use, some of this information are stored within the
+ * candidate itself, instead of always being dynamically computed. A single
+ * node can be valid placement candidate, as well as it is possible for a
+ * candidate to contain all the nodes of the host. The fewer nodes there
+ * are in a candidate, the better performance a domain placed onto it
+ * should get (at least from a NUMA point of view). For instance, looking
+ * for a numa candidates with 2GB of free memory means we want the subsets
+ * of the host NUMA nodes with, cumulatively, at least 2GB of free memory.
+ * This condition can be satisfied by just one particular node, or it may
+ * require more nodes, depending on the characteristics of the host, on how
+ * many domains have been created already, on how big they are, etc.
+ *
+ * The intended usage is as follows:
+ * 1. fist of all, call libxl__get_numa_candidates(), and specify the proper
+ * constraints to it (e.g., the amount of memory a domain need as the
+ * minimum amount of free memory for the candidates). If a candidate
+ * comparison function is provided, the candidate with fewer nodes that
+ * is found to be best according to what such fucntion says is returned.
+ * If no comparison function is passed, the very first candidate is.
+ * 2. The chosen candidate's nodemap should be utilized for computing the
+ * actual affinity of the domain which, given the current NUMA support
+ * in the hypervisor, is what determines the placement of the domain's
+ * vcpus and memory.
+ */
+
+typedef struct {
+ int nr_cpus, nr_nodes;
+ int nr_vcpus;
+ uint32_t free_memkb;
+ libxl_bitmap nodemap;
+} libxl__numa_candidate;
+
+/* Signature for the comparison function between two candidates */
+typedef int (*libxl__numa_candidate_cmpf)(const libxl__numa_candidate *c1,
+ const libxl__numa_candidate *c2);
+
+/*
+ * This looks for the best NUMA placement candidate satisfying some
+ * specific conditions. If min_nodes and/or max_nodes are not 0, their
+ * value is used to determine the minimum and maximum number of nodes the
+ * candidate can have. If they are 0, it means the candidate can contain
+ * from 1 node (min_nodes=0) to the total number of nodes of the host
+ * (max_ndoes=0). If min_free_memkb and/or min_cpus are not 0, the caller
+ * only wants candidates with at least the amount of free memory and the
+ * number of cpus they specify, respectively. If they are 0, the
+ * candidates' free memory and/or number of cpus won't be checked at all.
+ *
+ * Candidates are compared among each others by calling numa_cmpf(), which
+ * is where the heuristics for determining which candidate is the best
+ * one is actually implemented. The only bit of it that is hardcoded in
+ * this function is the fact that candidates with fewer nodes are always
+ * preferrable.
+ *
+ * If at least one suitable candidate is found, it is returned in cndt_out,
+ * cndt_found is set to one, and the function returns successfully. On the
+ * other hand, if not even one single candidate can be found, the function
+ * still returns successfully but cndt_found will be zero.
+ *
+ * It is up to the function to properly allocate cndt_out (by calling
+ * libxl__numa_candidate_alloc()), while it is the caller that should init
+ * (libxl__numa_candidate_init()) and free (libxl__numa_candidate_dispose())
+ * it.
+ */
+_hidden int libxl__get_numa_candidate(libxl__gc *gc,
+ uint32_t min_free_memkb, int min_cpus,
+ int min_nodes, int max_nodes,
+ libxl__numa_candidate_cmpf numa_cmpf,
+ libxl__numa_candidate *cndt_out,
+ int *cndt_found);
+
+/* Initialization, allocation and deallocation for placement candidates */
+static inline void libxl__numa_candidate_init(libxl__numa_candidate *cndt)
+{
+ cndt->free_memkb = 0;
+ cndt->nr_cpus = cndt->nr_nodes = cndt->nr_vcpus = 0;
+ libxl_bitmap_init(&cndt->nodemap);
+}
+
+static inline int libxl__numa_candidate_alloc(libxl__gc *gc,
+ libxl__numa_candidate *cndt)
+{
+ return libxl_node_bitmap_alloc(CTX, &cndt->nodemap, 0);
+}
+static inline void libxl__numa_candidate_dispose(libxl__numa_candidate *cndt)
+{
+ libxl_bitmap_dispose(&cndt->nodemap);
+}
+
+/* Retrieve (in nodemap) the node map associated to placement candidate cndt */
+static inline
+void libxl__numa_candidate_get_nodemap(libxl__gc *gc,
+ const libxl__numa_candidate *cndt,
+ libxl_bitmap *nodemap)
+{
+ libxl_bitmap_copy(CTX, nodemap, &cndt->nodemap);
+}
+/* Set the node map of placement candidate cndt to match nodemap */
+static inline
+void libxl__numa_candidate_put_nodemap(libxl__gc *gc,
+ libxl__numa_candidate *cndt,
+ const libxl_bitmap *nodemap)
+{
+ libxl_bitmap_copy(CTX, &cndt->nodemap, nodemap);
+}
/*
* Inserts "elm_new" into the sorted list "head".
diff --git a/tools/libxl/libxl_numa.c b/tools/libxl/libxl_numa.c
new file mode 100644
--- /dev/null
+++ b/tools/libxl/libxl_numa.c
@@ -0,0 +1,426 @@
+/*
+ * Copyright (C) 2012 Citrix Ltd.
+ * Author Dario Faggioli <dario.faggioli@xxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Lesser General Public License for more details.
+ */
+
+#include "libxl_osdeps.h" /* must come before any other headers */
+
+#include <glob.h>
+
+#include "libxl_internal.h"
+
+/*
+ * What follows are helpers for generating all the k-combinations
+ * without repetitions of a set S with n elements in it. Formally
+ * speaking, they are subsets of k distinct elements of S and, if
+ * S is n elements big, the number of k-combinations is equal to the
+ * binomial coefficient C(n k)=n!/(k! * (n - k)!).
+ *
+ * The various subset are generated one after the other by calling
+ * comb_init() first, and, after that, comb_next()
+ * C(n k)-1 times. An iterator is used to store the current status
+ * of the whole generation operation (i.e., basically, the last
+ * combination that has been generated). As soon as all combinations
+ * have been generated, comb_next() will start returning 0 instead of
+ * 1. The same instance of the iterator and the same values for
+ * n and k _must_ be used for each call (if that doesn't happen, the
+ * result is unspecified).
+ *
+ * The algorithm is a well known one (see, for example, D. Knuth's "The
+ * Art of Computer Programming - Volume 4, Fascicle 3" and it produces
+ * the combinations in such a way that they (well, more precisely, their
+ * indexes it the array/map representing the set) come with lexicographic
+ * ordering.
+ *
+ * For example, with n = 5 and k = 3, calling comb_init()
+ * will generate { 0, 1, 2 }, while subsequent valid calls to
+ * comb_next() will produce the following:
+ * { { 0, 1, 3 }, { 0, 1, 4 },
+ * { 0, 2, 3 }, { 0, 2, 4 }, { 0, 3, 4 },
+ * { 1, 2, 3 }, { 1, 2, 4 }, { 1, 3, 4 },
+ * { 2, 3, 4 } }
+ *
+ * This is used by the automatic NUMA placement logic below.
+ */
+typedef int* comb_iter_t;
+
+static int comb_init(libxl__gc *gc, comb_iter_t *it, int n, int k)
+{
+ comb_iter_t new_iter;
+ int i;
+
+ if (n < k)
+ return 0;
+
+ /* First set is always { 0, 1, 2, ..., k-1 } */
+ GCNEW_ARRAY(new_iter, k);
+ for (i = 0; i < k; i++)
+ new_iter[i] = i;
+
+ *it = new_iter;
+ return 1;
+}
+
+static int comb_next(comb_iter_t it, int n, int k)
+{
+ int i;
+
+ /*
+ * The idea here is to find the leftmost element from where
+ * we should start incrementing the indexes of the iterator.
+ * This means looking for the highest index that can be increased
+ * while still producing value smaller than n-1. In the example
+ * above, when dealing with { 0, 1, 4 }, such an element is the
+ * second one, as the third is already equal to 4 (which actually
+ * is n-1).
+ * Once we found from where to start, we increment that element
+ * and override the right-hand rest of the iterator with its
+ * successors, thus achieving lexicographic ordering.
+ *
+ * Regarding the termination of the generation process, when we
+ * manage in bringing n-k at the very first position of the iterator,
+ * we know that is the last valid combination ( { 2, 3, 4 }, with
+ * n - k = 5 - 2 = 2, in the example above), and thus we start
+ * returning 0 as soon as we cross that border.
+ */
+ for (i = k - 1; it[i] == n - k + i; i--) {
+ if (i <= 0)
+ return 0;
+ }
+ for (it[i]++, i++; i < k; i++)
+ it[i] = it[i - 1] + 1;
+ return 1;
+}
+
+/* NUMA automatic placement (see libxl_internal.h for details) */
+
+/*
+ * This function turns a k-combination iterator into a node map.
+ * This means the bits in the node map corresponding to the indexes
+ * of the given combination are the ones that will be set.
+ * For example, if the iterator represents the combination { 0, 2, 4},
+ * the node map will have bits #0, #2 and #4 set.
+ */
+static void comb_get_nodemap(comb_iter_t it, libxl_bitmap *nodemap, int k)
+{
+ int i;
+
+ libxl_bitmap_set_none(nodemap);
+ for (i = 0; i < k; i++)
+ libxl_bitmap_set(nodemap, it[i]);
+}
+
+/* Retrieve the number of cpus that the nodes that are part of the nodemap
+ * span. */
+static int nodemap_to_nr_cpus(libxl_cputopology *tinfo, int nr_cpus,
+ const libxl_bitmap *nodemap)
+{
+ int i, nodes_cpus = 0;
+
+ for (i = 0; i < nr_cpus; i++) {
+ if (libxl_bitmap_test(nodemap, tinfo[i].node))
+ nodes_cpus++;
+ }
+ return nodes_cpus;
+}
+
+/* Retrieve the amount of free memory within the nodemap */
+static uint32_t nodemap_to_free_memkb(libxl_numainfo *ninfo,
+ libxl_bitmap *nodemap)
+{
+ uint32_t free_memkb = 0;
+ int i;
+
+ libxl_for_each_set_bit(i, *nodemap)
+ free_memkb += ninfo[i].free / 1024;
+
+ return free_memkb;
+}
+
+/* Retrieve the number of vcpus able to run on the cpus of the nodes
+ * that are part of the nodemap. */
+static int nodemap_to_nr_vcpus(libxl__gc *gc, libxl_cputopology *tinfo,
+ const libxl_bitmap *nodemap)
+{
+ libxl_dominfo *dinfo = NULL;
+ libxl_bitmap vcpu_nodemap;
+ int nr_doms, nr_cpus;
+ int nr_vcpus = 0;
+ int i, j, k;
+
+ dinfo = libxl_list_domain(CTX, &nr_doms);
+ if (dinfo == NULL)
+ return ERROR_FAIL;
+
+ if (libxl_node_bitmap_alloc(CTX, &vcpu_nodemap, 0) < 0) {
+ libxl_dominfo_list_free(dinfo, nr_doms);
+ return ERROR_FAIL;
+ }
+
+ for (i = 0; i < nr_doms; i++) {
+ libxl_vcpuinfo *vinfo;
+ int nr_dom_vcpus;
+
+ vinfo = libxl_list_vcpu(CTX, dinfo[i].domid, &nr_dom_vcpus, &nr_cpus);
+ if (vinfo == NULL)
+ continue;
+
+ /* For each vcpu of each domain ... */
+ for (j = 0; j < nr_dom_vcpus; j++) {
+
+ /* Build up a map telling on which nodes the vcpu is runnable on */
+ libxl_bitmap_set_none(&vcpu_nodemap);
+ libxl_for_each_set_bit(k, vinfo[j].cpumap)
+ libxl_bitmap_set(&vcpu_nodemap, tinfo[k].node);
+
+ /* And check if that map has any intersection with our nodemap */
+ libxl_for_each_set_bit(k, vcpu_nodemap) {
+ if (libxl_bitmap_test(nodemap, k)) {
+ nr_vcpus++;
+ break;
+ }
+ }
+ }
+
+ libxl_vcpuinfo_list_free(vinfo, nr_dom_vcpus);
+ }
+
+ libxl_bitmap_dispose(&vcpu_nodemap);
+ libxl_dominfo_list_free(dinfo, nr_doms);
+ return nr_vcpus;
+}
+
+/*
+ * This function tries to figure out if the host has a consistent number
+ * of cpus along all its NUMA nodes. In fact, if that is the case, we can
+ * calculate the minimum number of nodes needed for a domain by just
+ * dividing its total number of vcpus by this value computed here.
+ * However, we are not allowed to assume that all the nodes have the
+ * same number of cpus. Therefore, in case discrepancies among different
+ * nodes are found, this function just returns 0, for the caller to know
+ * it shouldn't rely on this 'optimization', and sort out things in some
+ * other way (by doing something basic, like starting trying with candidates
+ * with just one node).
+ */
+static int count_cpus_per_node(libxl_cputopology *tinfo, int nr_cpus,
+ libxl_numainfo *ninfo, int nr_nodes)
+{
+ int cpus_per_node = 0;
+ int j, i;
+
+ /* This makes sense iff # of PCPUs is the same for all nodes */
+ for (j = 0; j < nr_nodes; j++) {
+ int curr_cpus = 0;
+
+ for (i = 0; i < nr_cpus; i++) {
+ if (tinfo[i].node == j)
+ curr_cpus++;
+ }
+ /* So, if the above does not hold, turn the whole thing off! */
+ cpus_per_node = cpus_per_node == 0 ? curr_cpus : cpus_per_node;
+ if (cpus_per_node != curr_cpus)
+ return 0;
+ }
+ return cpus_per_node;
+}
+
+/*
+ * Looks for the placement candidates that satisfyies some specific
+ * conditions and return the best one according to the provided
+ * comparison function.
+ */
+int libxl__get_numa_candidate(libxl__gc *gc,
+ uint32_t min_free_memkb, int min_cpus,
+ int min_nodes, int max_nodes,
+ libxl__numa_candidate_cmpf numa_cmpf,
+ libxl__numa_candidate *cndt_out,
+ int *cndt_found)
+{
+ libxl__numa_candidate new_cndt;
+ libxl_cputopology *tinfo = NULL;
+ libxl_numainfo *ninfo = NULL;
+ int nr_nodes = 0, nr_cpus = 0;
+ libxl_bitmap nodemap;
+ int rc = 0;
+
+ libxl_bitmap_init(&nodemap);
+ libxl__numa_candidate_init(&new_cndt);
+
+ /* Get platform info and prepare the map for testing the combinations */
+ ninfo = libxl_get_numainfo(CTX, &nr_nodes);
+ if (ninfo == NULL)
+ return ERROR_FAIL;
+
+ /*
+ * The good thing about this solution is that it is based on heuristics
+ * (implemented in numa_cmpf() ), but we at least can evaluate it on
+ * all the possible placement candidates. That can happen because the
+ * number of nodes present in current NUMA systems is quite small.
+ * In fact, even if a sum of binomials is involved, if the system has
+ * up to 8 nodes it "only" takes 256 steps. At the same time, 8 is a
+ * sensible value, as it is exactly the number of nodes the biggest
+ * NUMA systems provide at the time of this writing (and will probably
+ * continue to do so for a while). However, computanional complexity
+ * would explode on systems much bigger than that. 16 nodes system would
+ * still be fine (it will be 65536 steps), but it's really importante we
+ * avoid trying to run this on monsters with 32, 64 or more nodes (if
+ * they ever pop into being). Therefore, here it comes a safety catch
+ * that disables the algorithm for the cases when it wouldn't work well.
+ */
+ if (nr_nodes > 8) {
+ /* Log we did nothing and return 0, as no real error occurred */
+ LOG(WARN, "System has %d NUMA nodes, which is too big for the "
+ "placement algorithm to work effectively. Skipping it",
+ nr_nodes);
+ *cndt_found = 0;
+ goto out;
+ }
+
+ tinfo = libxl_get_cpu_topology(CTX, &nr_cpus);
+ if (tinfo == NULL) {
+ rc = ERROR_FAIL;
+ goto out;
+ }
+
+ rc = libxl_node_bitmap_alloc(CTX, &nodemap, 0);
+ if (rc)
+ goto out;
+ rc = libxl__numa_candidate_alloc(gc, &new_cndt);
+ if (rc)
+ goto out;
+
+ /*
+ * If the minimum number of NUMA nodes is not explicitly specified
+ * (i.e., min_nodes == 0), we try to figure out a sensible number of nodes
+ * from where to start generating candidates, if possible (or just start
+ * from 1 otherwise). The maximum number of nodes should not exceed the
+ * number of existent NUMA nodes on the host, or the candidate generation
+ * won't work properly.
+ */
+ if (!min_nodes) {
+ int cpus_per_node;
+
+ cpus_per_node = count_cpus_per_node(tinfo, nr_cpus, ninfo, nr_nodes);
+ if (cpus_per_node == 0)
+ min_nodes = 1;
+ else
+ min_nodes = (min_cpus + cpus_per_node - 1) / cpus_per_node;
+ }
+ if (min_nodes > nr_nodes)
+ min_nodes = nr_nodes;
+ if (!max_nodes || max_nodes > nr_nodes)
+ max_nodes = nr_nodes;
+ if (min_nodes > max_nodes) {
+ rc = ERROR_INVAL;
+ goto out;
+ }
+
+ /* This is up to the caller to be disposed */
+ rc = libxl__numa_candidate_alloc(gc, cndt_out);
+ if (rc)
+ goto out;
+
+ /*
+ * Consider all the combinations with sizes in [min_nodes, max_nodes]
+ * (see comb_init() and comb_next()). Note that, since the fewer the
+ * number of nodes the better, it is guaranteed that any candidate
+ * found during the i-eth step will be better than any other one we
+ * could find during the (i+1)-eth and all the subsequent steps (they
+ * all will have more nodes). It's thus pointless to keep going if
+ * we already found something.
+ */
+ *cndt_found = 0;
+ while (min_nodes <= max_nodes && *cndt_found == 0) {
+ comb_iter_t comb_iter;
+ int comb_ok;
+
+ /*
+ * And here it is. Each step of this cycle generates a combination of
+ * nodes as big as min_nodes mandates. Each of these combinations is
+ * checked against the constraints provided by the caller (namely,
+ * amount of free memory and number of cpus) and it can concur to
+ * become our best placement iff it passes the check.
+ */
+ for (comb_ok = comb_init(gc, &comb_iter, nr_nodes, min_nodes); comb_ok;
+ comb_ok = comb_next(comb_iter, nr_nodes, min_nodes)) {
+ uint32_t nodes_free_memkb;
+ int nodes_cpus;
+
+ comb_get_nodemap(comb_iter, &nodemap, min_nodes);
+
+ /* If there is not enough memory in this combination, skip it
+ * and go generating the next one... */
+ nodes_free_memkb = nodemap_to_free_memkb(ninfo, &nodemap);
+ if (min_free_memkb && nodes_free_memkb < min_free_memkb)
+ continue;
+
+ /* And the same applies if this combination is short in cpus */
+ nodes_cpus = nodemap_to_nr_cpus(tinfo, nr_cpus, &nodemap);
+ if (min_cpus && nodes_cpus < min_cpus)
+ continue;
+
+ /*
+ * Conditions are met, we can compare this candidate with the
+ * current best one (if any).
+ */
+ libxl__numa_candidate_put_nodemap(gc, &new_cndt, &nodemap);
+ new_cndt.nr_vcpus = nodemap_to_nr_vcpus(gc, tinfo, &nodemap);
+ new_cndt.free_memkb = nodes_free_memkb;
+ new_cndt.nr_nodes = min_nodes;
+ new_cndt.nr_cpus = nodes_cpus;
+
+ /*
+ * Check if the new candidate we is better the what we found up
+ * to now by means of the comparison function. If no comparison
+ * function is provided, just return as soon as we find our first
+ * candidate.
+ */
+ if (*cndt_found == 0 || numa_cmpf(&new_cndt, cndt_out) < 0) {
+ *cndt_found = 1;
+
+ LOG(DEBUG, "New best NUMA placement candidate found: "
+ "nr_nodes=%d, nr_cpus=%d, nr_vcpus=%d, "
+ "free_memkb=%"PRIu32"", min_nodes, new_cndt.nr_cpus,
+ new_cndt.nr_vcpus, new_cndt.free_memkb / 1024);
+
+ libxl__numa_candidate_put_nodemap(gc, cndt_out, &nodemap);
+ cndt_out->nr_vcpus = new_cndt.nr_vcpus;
+ cndt_out->free_memkb = new_cndt.free_memkb;
+ cndt_out->nr_nodes = new_cndt.nr_nodes;
+ cndt_out->nr_cpus = new_cndt.nr_cpus;
+
+ if (numa_cmpf == NULL)
+ break;
+ }
+ }
+ min_nodes++;
+ }
+
+ if (*cndt_found == 0)
+ LOG(NOTICE, "NUMA placement failed, performance might be affected");
+
+ out:
+ libxl_bitmap_dispose(&nodemap);
+ libxl__numa_candidate_dispose(&new_cndt);
+ libxl_numainfo_list_free(ninfo, nr_nodes);
+ libxl_cputopology_list_free(tinfo, nr_cpus);
+ return rc;
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
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