Re: libxc: maintain a small, per-handle, cache of hypercall buffer memory (Was: Re: Xen 4.1 rc1 test report)

[Haitao Shan <maillists.shan@gmail.com>]

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I have tested the patch. The bug can be fixed by Ian's patch. Thanks!

So, Ian, please go on the process of your submitting the patch.

Shan Haitao

2011/1/31 Haitao Shan <maillists.shan@gmail.com>

> Thanks, Ian.
> I will test tomorrow and let you know the result.
>
> Shan Haitao
>
> 2011/1/31 Ian Campbell <Ian.Campbell@eu.citrix.com>
>
>> On Mon, 2011-01-31 at 08:57 +0000, Haitao Shan wrote:
>>
>> > And BTW: I am using c/s 22846.
>>
>> Sorry, I didn't notice a patch which I was holding off for 4.2 in my
>> queue before this one.
>>
>> Version rebased onto 22846:52e928af3637 below.
>>
>> Ian.
>>
>> 8<---------------------------------------
>>
>> # HG changeset patch
>> # User Ian Campbell <ian.campbell@citrix.com>
>> # Date 1296466278 0
>> # Node ID 9e6175469e6f246ee9370ef57f987bb435b00bef
>> # Parent  5b6663ba2bb2c54e8fa6745afa16297ebe43328d
>> 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.
>>
>> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
>>
>> diff -r 5b6663ba2bb2 -r 9e6175469e6f tools/libxc/xc_hcall_buf.c
>> --- a/tools/libxc/xc_hcall_buf.c        Mon Jan 31 09:14:52 2011 +0000
>> +++ b/tools/libxc/xc_hcall_buf.c        Mon Jan 31 09:31:18 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);
>> +        p = memalign(PAGE_SIZE, size);
>>  #endif
>>
>> -    if (!p)
>> -        return NULL;
>> +        if (!p)
>> +            return NULL;
>>
>>  #ifndef __sun__
>> -    if ( mlock(p, size) < 0 )
>> -    {
>> -        free(p);
>> -        return NULL;
>> +        if ( mlock(p, size) < 0 )
>> +        {
>> +            free(p);
>> +            return NULL;
>> +        }
>> +#endif
>>     }
>> -#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 5b6663ba2bb2 -r 9e6175469e6f tools/libxc/xc_private.c
>> --- a/tools/libxc/xc_private.c  Mon Jan 31 09:14:52 2011 +0000
>> +++ b/tools/libxc/xc_private.c  Mon Jan 31 09:31:18 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 5b6663ba2bb2 -r 9e6175469e6f tools/libxc/xc_private.h
>> --- a/tools/libxc/xc_private.h  Mon Jan 31 09:14:52 2011 +0000
>> +++ b/tools/libxc/xc_private.h  Mon Jan 31 09:31:18 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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