Mailing List Archive

# HG changeset patch
# User Ian Campbell <ian.campbell@citrix.com>
# Date 1296588396 0
# Node ID 9a6458e0c3f5b68aac347c2e8c60e7732f70d959
# Parent 74cd0f668546d14b5965d8f1e715da1662915646
libxc: maintain a small, per-handle, cache of hypercall buffer memory

Constantly m(un)locking memory can have significant overhead on
systems with large numbers of CPUs. This was previously fixed by
20841:fbe8f32fa257 but this was dropped during the transition to
hypercall buffers.

Introduce a small cache of single page hypercall buffer allocations
which can be resused to avoid this overhead.

Add some statistics tracking to the hypercall buffer allocations.

The cache size of 4 was chosen based on these statistics since they
indicated that 2 pages was sufficient to satisfy all concurrent single
page hypercall buffer allocations seen during "xl create", "xl
shutdown" and "xl destroy" of both a PV and HVM guest therefore 4
pages should cover the majority of important cases.

This fixes http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1719.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reported-by: Zheng, Shaohui <shaohui.zheng@intel.com>
Tested-by: Haitao Shan <maillists.shan@gmail.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>
---
tools/libxc/xc_hcall_buf.c | 148 ++++++++++++++++++++++++++++++++++++++-------
tools/libxc/xc_private.c | 12 +++
tools/libxc/xc_private.h | 27 ++++++++
3 files changed, 165 insertions(+), 22 deletions(-)

diff -r 74cd0f668546 -r 9a6458e0c3f5 tools/libxc/xc_hcall_buf.c
--- a/tools/libxc/xc_hcall_buf.c Tue Feb 01 19:25:08 2011 +0000
+++ b/tools/libxc/xc_hcall_buf.c Tue Feb 01 19:26:36 2011 +0000
@@ -18,6 +18,7 @@

#include <stdlib.h>
#include <malloc.h>
+#include <pthread.h>

#include "xc_private.h"
#include "xg_private.h"
@@ -28,31 +29,137 @@ xc_hypercall_buffer_t XC__HYPERCALL_BUFF
HYPERCALL_BUFFER_INIT_NO_BOUNCE
};

+pthread_mutex_t hypercall_buffer_cache_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+static void hypercall_buffer_cache_lock(xc_interface *xch)
+{
+ if ( xch->flags & XC_OPENFLAG_NON_REENTRANT )
+ return;
+ pthread_mutex_lock(&hypercall_buffer_cache_mutex);
+}
+
+static void hypercall_buffer_cache_unlock(xc_interface *xch)
+{
+ if ( xch->flags & XC_OPENFLAG_NON_REENTRANT )
+ return;
+ pthread_mutex_unlock(&hypercall_buffer_cache_mutex);
+}
+
+static void *hypercall_buffer_cache_alloc(xc_interface *xch, int nr_pages)
+{
+ void *p = NULL;
+
+ hypercall_buffer_cache_lock(xch);
+
+ xch->hypercall_buffer_total_allocations++;
+ xch->hypercall_buffer_current_allocations++;
+ if ( xch->hypercall_buffer_current_allocations > xch->hypercall_buffer_maximum_allocations )
+ xch->hypercall_buffer_maximum_allocations = xch->hypercall_buffer_current_allocations;
+
+ if ( nr_pages > 1 )
+ {
+ xch->hypercall_buffer_cache_toobig++;
+ }
+ else if ( xch->hypercall_buffer_cache_nr > 0 )
+ {
+ p = xch->hypercall_buffer_cache[--xch->hypercall_buffer_cache_nr];
+ xch->hypercall_buffer_cache_hits++;
+ }
+ else
+ {
+ xch->hypercall_buffer_cache_misses++;
+ }
+
+ hypercall_buffer_cache_unlock(xch);
+
+ return p;
+}
+
+static int hypercall_buffer_cache_free(xc_interface *xch, void *p, int nr_pages)
+{
+ int rc = 0;
+
+ hypercall_buffer_cache_lock(xch);
+
+ xch->hypercall_buffer_total_releases++;
+ xch->hypercall_buffer_current_allocations--;
+
+ if ( nr_pages == 1 && xch->hypercall_buffer_cache_nr < HYPERCALL_BUFFER_CACHE_SIZE )
+ {
+ xch->hypercall_buffer_cache[xch->hypercall_buffer_cache_nr++] = p;
+ rc = 1;
+ }
+
+ hypercall_buffer_cache_unlock(xch);
+
+ return rc;
+}
+
+static void do_hypercall_buffer_free_pages(void *ptr, int nr_pages)
+{
+#ifndef __sun__
+ (void) munlock(ptr, nr_pages * PAGE_SIZE);
+#endif
+
+ free(ptr);
+}
+
+void xc__hypercall_buffer_cache_release(xc_interface *xch)
+{
+ void *p;
+
+ hypercall_buffer_cache_lock(xch);
+
+ DBGPRINTF("hypercall buffer: total allocations:%d total releases:%d",
+ xch->hypercall_buffer_total_allocations,
+ xch->hypercall_buffer_total_releases);
+ DBGPRINTF("hypercall buffer: current allocations:%d maximum allocations:%d",
+ xch->hypercall_buffer_current_allocations,
+ xch->hypercall_buffer_maximum_allocations);
+ DBGPRINTF("hypercall buffer: cache current size:%d",
+ xch->hypercall_buffer_cache_nr);
+ DBGPRINTF("hypercall buffer: cache hits:%d misses:%d toobig:%d",
+ xch->hypercall_buffer_cache_hits,
+ xch->hypercall_buffer_cache_misses,
+ xch->hypercall_buffer_cache_toobig);
+
+ while ( xch->hypercall_buffer_cache_nr > 0 )
+ {
+ p = xch->hypercall_buffer_cache[--xch->hypercall_buffer_cache_nr];
+ do_hypercall_buffer_free_pages(p, 1);
+ }
+
+ hypercall_buffer_cache_unlock(xch);
+}
+
void *xc__hypercall_buffer_alloc_pages(xc_interface *xch, xc_hypercall_buffer_t *b, int nr_pages)
{
size_t size = nr_pages * PAGE_SIZE;
- void *p;
+ void *p = hypercall_buffer_cache_alloc(xch, nr_pages);
+
+ if ( !p ) {
#if defined(_POSIX_C_SOURCE) && !defined(__sun__)
- int ret;
- ret = posix_memalign(&p, PAGE_SIZE, size);
- if (ret != 0)
- return NULL;
+ int ret;
+ ret = posix_memalign(&p, PAGE_SIZE, size);
+ if (ret != 0)
+ return NULL;
#elif defined(__NetBSD__) || defined(__OpenBSD__)
- p = valloc(size);
+ p = valloc(size);
#else
- p = memalign(PAGE_SIZE, size);
-#endif
-
- if (!p)
- return NULL;
+ p = memalign(PAGE_SIZE, size);
+#endif
+
+ if (!p)
+ return NULL;

#ifndef __sun__
- if ( mlock(p, size) < 0 )
- {
- free(p);
- return NULL;
- }
-#endif
+ if ( mlock(p, size) < 0 )
+ {
+ free(p);
+ return NULL;
+ }
+#endif
+ }

b->hbuf = p;

@@ -65,11 +172,8 @@ void xc__hypercall_buffer_free_pages(xc_
if ( b->hbuf == NULL )
return;

-#ifndef __sun__
- (void) munlock(b->hbuf, nr_pages * PAGE_SIZE);
-#endif
-
- free(b->hbuf);
+ if ( !hypercall_buffer_cache_free(xch, b->hbuf, nr_pages) )
+ do_hypercall_buffer_free_pages(b->hbuf, nr_pages);
}

struct allocation_header {
diff -r 74cd0f668546 -r 9a6458e0c3f5 tools/libxc/xc_private.c
--- a/tools/libxc/xc_private.c Tue Feb 01 19:25:08 2011 +0000
+++ b/tools/libxc/xc_private.c Tue Feb 01 19:26:36 2011 +0000
@@ -126,6 +126,16 @@ static struct xc_interface_core *xc_inte
xch->error_handler = logger; xch->error_handler_tofree = 0;
xch->dombuild_logger = dombuild_logger; xch->dombuild_logger_tofree = 0;

+ xch->hypercall_buffer_cache_nr = 0;
+
+ xch->hypercall_buffer_total_allocations = 0;
+ xch->hypercall_buffer_total_releases = 0;
+ xch->hypercall_buffer_current_allocations = 0;
+ xch->hypercall_buffer_maximum_allocations = 0;
+ xch->hypercall_buffer_cache_hits = 0;
+ xch->hypercall_buffer_cache_misses = 0;
+ xch->hypercall_buffer_cache_toobig = 0;
+
xch->ops_handle = XC_OSDEP_OPEN_ERROR;
xch->ops = NULL;

@@ -171,6 +181,8 @@ static int xc_interface_close_common(xc_
static int xc_interface_close_common(xc_interface *xch)
{
int rc = 0;
+
+ xc__hypercall_buffer_cache_release(xch);

xtl_logger_destroy(xch->dombuild_logger_tofree);
xtl_logger_destroy(xch->error_handler_tofree);
diff -r 74cd0f668546 -r 9a6458e0c3f5 tools/libxc/xc_private.h
--- a/tools/libxc/xc_private.h Tue Feb 01 19:25:08 2011 +0000
+++ b/tools/libxc/xc_private.h Tue Feb 01 19:26:36 2011 +0000
@@ -75,6 +75,28 @@ struct xc_interface_core {
FILE *dombuild_logger_file;
const char *currently_progress_reporting;

+ /*
+ * A simple cache of unused, single page, hypercall buffers
+ *
+ * Protected by a global lock.
+ */
+#define HYPERCALL_BUFFER_CACHE_SIZE 4
+ int hypercall_buffer_cache_nr;
+ void *hypercall_buffer_cache[HYPERCALL_BUFFER_CACHE_SIZE];
+
+ /*
+ * Hypercall buffer statistics. All protected by the global
+ * hypercall_buffer_cache lock.
+ */
+ int hypercall_buffer_total_allocations;
+ int hypercall_buffer_total_releases;
+ int hypercall_buffer_current_allocations;
+ int hypercall_buffer_maximum_allocations;
+ int hypercall_buffer_cache_hits;
+ int hypercall_buffer_cache_misses;
+ int hypercall_buffer_cache_toobig;
+
+ /* Low lovel OS interface */
xc_osdep_info_t osdep;
xc_osdep_ops *ops; /* backend operations */
xc_osdep_handle ops_handle; /* opaque data for xc_osdep_ops */
@@ -156,6 +178,11 @@ int xc__hypercall_bounce_pre(xc_interfac
#define xc_hypercall_bounce_pre(_xch, _name) xc__hypercall_bounce_pre(_xch, HYPERCALL_BUFFER(_name))
void xc__hypercall_bounce_post(xc_interface *xch, xc_hypercall_buffer_t *bounce);
#define xc_hypercall_bounce_post(_xch, _name) xc__hypercall_bounce_post(_xch, HYPERCALL_BUFFER(_name))
+
+/*
+ * Release hypercall buffer cache
+ */
+void xc__hypercall_buffer_cache_release(xc_interface *xch);

/*
* Hypercall interfaces.

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