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Re: [Xen-devel] [PATCH V4] Switch from select() to poll() in xenconsoled's IO loop
On 07/01/13 14:28, Wei Liu wrote:
In Linux select() typically supports up to 1024 file descriptors. This can be
a problem when user tries to boot up many guests. Switching to poll() has
minimum impact on existing code and has better scalibility.
pollfd array is dynamically allocated / reallocated. If the array fails to
expand, we just ignore the incoming fd.
Change from V2:
* remove unnecessary malloc in initialize_pollfd_arrays
* use ROUND_UP to get new size of arrays
Change from V3:
* remove initialize and destroy function for array
* embedded tracking structure in struct domain, eliminate fd_to_pollfd
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
tools/console/daemon/io.c | 119 ++++++++++++++++++++++++++++--------------
tools/console/daemon/utils.c | 2 +
tools/console/daemon/utils.h | 2 +
3 files changed, 85 insertions(+), 38 deletions(-)
diff --git a/tools/console/daemon/io.c b/tools/console/daemon/io.c
index 48fe151..80f7144 100644
--- a/tools/console/daemon/io.c
+++ b/tools/console/daemon/io.c
@@ -28,7 +28,7 @@
#include <stdlib.h>
#include <errno.h>
#include <string.h>
-#include <sys/select.h>
+#include <poll.h>
#include <fcntl.h>
#include <unistd.h>
#include <termios.h>
@@ -69,6 +69,7 @@ static int log_hv_fd = -1;
static evtchn_port_or_error_t log_hv_evtchn = -1;
static xc_interface *xch; /* why does xenconsoled have two xc handles ? */
static xc_evtchn *xce_handle = NULL;
+static struct pollfd *xce_pollfd = NULL;
struct buffer {
char *data;
@@ -81,7 +82,9 @@ struct buffer {
struct domain {
int domid;
int master_fd;
+ struct pollfd *master_pollfd;
int slave_fd;
+ struct pollfd *slave_pollfd;
int log_fd;
bool is_dead;
unsigned last_seen;
@@ -92,6 +95,7 @@ struct domain {
evtchn_port_or_error_t local_port;
evtchn_port_or_error_t remote_port;
xc_evtchn *xce_handle;
+ struct pollfd *xce_pollfd;
struct xencons_interface *interface;
int event_count;
long long next_period;
@@ -928,9 +932,52 @@ static void handle_log_reload(void)
}
}
+static struct pollfd *fds;
+static unsigned int current_array_size;
+static unsigned int nr_fds;
+
+#define ROUNDUP(_x,_w) (((unsigned long)(_x)+(1UL<<(_w))-1) & ~((1UL<<(_w))-1))
+static struct pollfd *set_fds(int fd, short events)
+{
+ struct pollfd *ret;
+ if (current_array_size < nr_fds + 1) {
+ struct pollfd *new_fds = NULL;
+ unsigned long newsize;
+
+ /* Round up to 2^8 boundary, in practice this just
+ * make newsize larger than current_array_size.
+ */
+ newsize = ROUNDUP(nr_fds + 1, 8);
+
+ new_fds = realloc(fds, sizeof(struct pollfd)*newsize);
+ if (!new_fds)
+ goto fail;
+ fds = new_fds;
+
+ memset(&fds[0] + current_array_size, 0,
+ sizeof(struct pollfd) * (newsize-current_array_size));
+ current_array_size = newsize;
+ }
+
+ fds[nr_fds].fd = fd;
+ fds[nr_fds].events = events;
+ ret = &fds[nr_fds];
+ nr_fds++;
+
+ return ret;
+fail:
+ dolog(LOG_ERR, "realloc failed, ignoring fd %d\n", fd);
+ return NULL;
+}
+
+static void reset_fds(void)
+{
+ nr_fds = 0;
+ memset(fds, 0, sizeof(struct pollfd) * current_array_size);
+}
+
void handle_io(void)
{
- fd_set readfds, writefds;
int ret;
if (log_hv) {
@@ -959,21 +1006,16 @@ void handle_io(void)
for (;;) {
struct domain *d, *n;
- int max_fd = -1;
- struct timeval timeout;
+ int poll_timeout; /* timeout in milliseconds */
struct timespec ts;
long long now, next_timeout = 0;
- FD_ZERO(&readfds);
- FD_ZERO(&writefds);
+ reset_fds();
- FD_SET(xs_fileno(xs), &readfds);
- max_fd = MAX(xs_fileno(xs), max_fd);
+ xs_pollfd = set_fds(xs_fileno(xs), POLLIN);
- if (log_hv) {
- FD_SET(xc_evtchn_fd(xce_handle), &readfds);
- max_fd = MAX(xc_evtchn_fd(xce_handle), max_fd);
- }
+ if (log_hv)
+ xce_pollfd = set_fds(xc_evtchn_fd(xce_handle), POLLIN);
if (clock_gettime(CLOCK_MONOTONIC, &ts) < 0)
return;
@@ -982,11 +1024,7 @@ void handle_io(void)
/* Re-calculate any event counter allowances & unblock
domains with new allowance */
for (d = dom_head; d; d = d->next) {
- /* Add 5ms of fuzz since select() often returns
- a couple of ms sooner than requested. Without
- the fuzz we typically do an extra spin in select()
- with a 1/2 ms timeout every other iteration */
- if ((now+5) > d->next_period) {
+ if (now > d->next_period) {
Is poll more accurate than select? I would have thought that they were
based on the same timing, and thus equally "fuzzy"?
d->next_period = now + RATE_LIMIT_PERIOD;
if (d->event_count >= RATE_LIMIT_ALLOWANCE) {
(void)xc_evtchn_unmask(d->xce_handle,
d->local_port);
@@ -1006,74 +1044,76 @@ void handle_io(void)
!d->buffer.max_capacity ||
d->buffer.size < d->buffer.max_capacity) {
int evtchn_fd =
xc_evtchn_fd(d->xce_handle);
- FD_SET(evtchn_fd, &readfds);
- max_fd = MAX(evtchn_fd, max_fd);
+ d->xce_pollfd = set_fds(evtchn_fd,
POLLIN);
}
}
if (d->master_fd != -1) {
+ short events = 0;
if (!d->is_dead && ring_free_bytes(d))
- FD_SET(d->master_fd, &readfds);
+ events |= POLLIN;
if (!buffer_empty(&d->buffer))
- FD_SET(d->master_fd, &writefds);
- max_fd = MAX(d->master_fd, max_fd);
+ events |= POLLOUT;
+
+ if (events)
+ d->master_pollfd =
+ set_fds(d->master_fd, events);
}
}
/* If any domain has been rate limited, we need to work
- out what timeout to supply to select */
+ out what timeout to supply to poll */
if (next_timeout) {
long long duration = (next_timeout - now);
if (duration <= 0) /* sanity check */
duration = 1;
- timeout.tv_sec = duration / 1000;
- timeout.tv_usec = ((duration - (timeout.tv_sec * 1000))
- * 1000);
+ poll_timeout = (int)duration;
}
- ret = select(max_fd + 1, &readfds, &writefds, 0,
- next_timeout ? &timeout : NULL);
+ ret = poll(fds, nr_fds, next_timeout ? poll_timeout : -1);
if (log_reload) {
handle_log_reload();
log_reload = 0;
}
- /* Abort if select failed, except for EINTR cases
+ /* Abort if poll failed, except for EINTR cases
which indicate a possible log reload */
if (ret == -1) {
if (errno == EINTR)
continue;
- dolog(LOG_ERR, "Failure in select: %d (%s)",
+ dolog(LOG_ERR, "Failure in poll: %d (%s)",
errno, strerror(errno));
break;
}
- if (log_hv && FD_ISSET(xc_evtchn_fd(xce_handle), &readfds))
+ if (log_hv && xce_pollfd && xce_pollfd->revents & POLLIN)
handle_hv_logs();
if (ret <= 0)
continue;
- if (FD_ISSET(xs_fileno(xs), &readfds))
+ if (xs_pollfd && xs_pollfd->revents & POLLIN)
handle_xs();
for (d = dom_head; d; d = n) {
n = d->next;
if (d->event_count < RATE_LIMIT_ALLOWANCE) {
if (d->xce_handle != NULL &&
- FD_ISSET(xc_evtchn_fd(d->xce_handle),
- &readfds))
+ d->xce_pollfd != NULL &&
+ d->xce_pollfd->revents & POLLIN)
handle_ring_read(d);
}
- if (d->master_fd != -1 && FD_ISSET(d->master_fd,
- &readfds))
+ if (d->master_fd != -1 &&
+ d->master_pollfd &&
+ d->master_pollfd->revents & POLLIN)
handle_tty_read(d);
- if (d->master_fd != -1 && FD_ISSET(d->master_fd,
- &writefds))
+ if (d->master_fd != -1 &&
+ d->master_pollfd &&
+ d->master_pollfd->revents & POLLOUT)
handle_tty_write(d);
if (d->last_seen != enum_pass)
@@ -1084,6 +1124,9 @@ void handle_io(void)
}
}
+ free(fds);
+ current_array_size = 0;
+
out:
if (log_hv_fd != -1) {
close(log_hv_fd);
diff --git a/tools/console/daemon/utils.c b/tools/console/daemon/utils.c
index aab6f42..d0b1b00 100644
--- a/tools/console/daemon/utils.c
+++ b/tools/console/daemon/utils.c
@@ -33,11 +33,13 @@
#include <sys/un.h>
#include <string.h>
#include <signal.h>
+#include <poll.h>
#include "xenctrl.h"
#include "utils.h"
struct xs_handle *xs;
+struct pollfd *xs_pollfd;
I don't see this used outside of io.c - am I missing something?
Adding more dependencies between different source files seems
unnecessary...
--
Mats
xc_interface *xc;
static void child_exit(int sig)
diff --git a/tools/console/daemon/utils.h b/tools/console/daemon/utils.h
index 8725dcd..8e72dab 100644
--- a/tools/console/daemon/utils.h
+++ b/tools/console/daemon/utils.h
@@ -24,6 +24,7 @@
#include <stdbool.h>
#include <syslog.h>
#include <stdio.h>
+#include <poll.h>
#include <xenctrl.h>
#include <xenstore.h>
@@ -32,6 +33,7 @@ void daemonize(const char *pidfile);
bool xen_setup(void);
extern struct xs_handle *xs;
+extern struct pollfd *xs_pollfd;
extern xc_interface *xc;
#if 1
--
1.7.10.4
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