[xen stable-4.17] credit2: respect credit2_runqueue=all when arranging runqueues

[patchbot@xxxxxxx]

commit 74b76704fd4059e9133e84c1384501858e9663b7
Author:     Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
AuthorDate: Fri Mar 3 07:57:39 2023 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Mar 3 07:57:39 2023 +0100

    credit2: respect credit2_runqueue=all when arranging runqueues
    
    Documentation for credit2_runqueue=all says it should create one queue
    for all pCPUs on the host. But since introduction
    sched_credit2_max_cpus_runqueue, it actually created separate runqueue
    per socket, even if the CPUs count is below
    sched_credit2_max_cpus_runqueue.
    
    Adjust the condition to skip syblink check in case of
    credit2_runqueue=all.
    
    Fixes: 8e2aa76dc167 ("xen: credit2: limit the max number of CPUs in a 
runqueue")
    Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    master commit: 1f5747ee929fbbcae58d7234c6c38a77495d0cfe
    master date: 2023-02-15 16:12:42 +0100
---
 docs/misc/xen-command-line.pandoc | 5 +++++
 xen/common/sched/credit2.c        | 9 +++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index 807ca51fb2..5be5ce10c6 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -726,6 +726,11 @@ Available alternatives, with their meaning, are:
 * `all`: just one runqueue shared by all the logical pCPUs of
          the host
 
+Regardless of the above choice, Xen attempts to respect
+`sched_credit2_max_cpus_runqueue` limit, which may mean more than one runqueue
+for the `all` value. If that isn't intended, raise
+the `sched_credit2_max_cpus_runqueue` value.
+
 ### dbgp
 > `= ehci[ <integer> | @pci<bus>:<slot>.<func> ]`
 > `= xhci[ <integer> | @pci<bus>:<slot>.<func> ][,share=<bool>|hwdom]`
diff --git a/xen/common/sched/credit2.c b/xen/common/sched/credit2.c
index 0e3f89e537..ae55feea34 100644
--- a/xen/common/sched/credit2.c
+++ b/xen/common/sched/credit2.c
@@ -996,9 +996,14 @@ cpu_add_to_runqueue(const struct scheduler *ops, unsigned 
int cpu)
              *
              * Otherwise, let's try to make sure that siblings stay in the
              * same runqueue, pretty much under any cinrcumnstances.
+             *
+             * Furthermore, try to respect credit2_runqueue=all, as long as
+             * max_cpus_runq isn't violated.
              */
-            if ( rqd->refcnt < max_cpus_runq && (ops->cpupool->gran != 
SCHED_GRAN_cpu ||
-                  cpu_runqueue_siblings_match(rqd, cpu, max_cpus_runq)) )
+            if ( rqd->refcnt < max_cpus_runq &&
+                 (ops->cpupool->gran != SCHED_GRAN_cpu ||
+                  cpu_runqueue_siblings_match(rqd, cpu, max_cpus_runq) ||
+                  opt_runqueue == OPT_RUNQUEUE_ALL) )
             {
                 /*
                  * This runqueue is ok, but as we said, we also want an even
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.17