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

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Mon, 2011-01-31 at 03:06 +0000, Haitao Shan wrote: 
> Hi, Ian,
> 
> I can not apply your patch. Is this patch developed against more newer
> version of Xen than what I can have at hand?

There was a typo below (an xc_hypercall_buffer_cache_release which
should have been xc__hypercall_buffer_cache_release) but it sounds like
you have trouble with actually applying the patch? 

It was against a recent xen-unstable on the day I posted it. What were
the rejects you saw?

If you have a particular version you want to test against I can generate
a suitable patch for you.

Ian.

> 
> Shan Haitao
> 
> 2011/1/26 Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>:
> > On Wed, 2011-01-26 at 00:47 +0000, Haitao Shan wrote:
> >> I think it is basically the same idea as Keir introduced in 20841. I
> >> guess this bug would happen on platforms which has large number of
> >> physical CPUs, not only on EX system of Intel.
> >> If you can cook the patch, that would be great! Thanks!!
> >
> > Does this help?
> >
> > Ian.
> >
> > 8<---------------------------------------
> >
> > # HG changeset patch
> > # User Ian Campbell <ian.campbell@xxxxxxxxxx>
> > # Date 1296038761 0
> > # Node ID 8b8b7e024f9d6f4c2ce1a4efbf38f07eeb460d91
> > # Parent  e4e69622dc95037eab6740f79ecf9c1d05bca529
> > 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 reused 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@xxxxxxxxxx>
> >
> > diff -r e4e69622dc95 -r 8b8b7e024f9d tools/libxc/xc_hcall_buf.c
> > --- a/tools/libxc/xc_hcall_buf.c        Wed Jan 26 10:22:42 2011 +0000
> > +++ b/tools/libxc/xc_hcall_buf.c        Wed Jan 26 10:46:01 2011 +0000
> > @@ -18,6 +18,7 @@
> >
> >  #include <stdlib.h>
> >  #include <string.h>
> > +#include <pthread.h>
> >
> >  #include "xc_private.h"
> >  #include "xg_private.h"
> > @@ -28,11 +29,108 @@ 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;
> > +}
> > +
> > +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];
> > +        xch->ops->u.privcmd.free_hypercall_buffer(xch, xch->ops_handle, p, 
> > 1);
> > +    }
> > +
> > +    hypercall_buffer_cache_unlock(xch);
> > +}
> > +
> >  void *xc__hypercall_buffer_alloc_pages(xc_interface *xch, 
> > xc_hypercall_buffer_t *b, int nr_pages)
> >  {
> > -    void *p = xch->ops->u.privcmd.alloc_hypercall_buffer(xch, 
> > xch->ops_handle, nr_pages);
> > +    void *p = hypercall_buffer_cache_alloc(xch, nr_pages);
> >
> > -    if (!p)
> > +    if ( !p )
> > +        p = xch->ops->u.privcmd.alloc_hypercall_buffer(xch, 
> > xch->ops_handle, nr_pages);
> > +
> > +    if ( !p )
> >         return NULL;
> >
> >     b->hbuf = p;
> > @@ -47,7 +145,8 @@ void xc__hypercall_buffer_free_pages(xc_
> >     if ( b->hbuf == NULL )
> >         return;
> >
> > -    xch->ops->u.privcmd.free_hypercall_buffer(xch, xch->ops_handle, 
> > b->hbuf, nr_pages);
> > +    if ( !hypercall_buffer_cache_free(xch, b->hbuf, nr_pages) )
> > +        xch->ops->u.privcmd.free_hypercall_buffer(xch, xch->ops_handle, 
> > b->hbuf, nr_pages);
> >  }
> >
> >  struct allocation_header {
> > diff -r e4e69622dc95 -r 8b8b7e024f9d tools/libxc/xc_private.c
> > --- a/tools/libxc/xc_private.c  Wed Jan 26 10:22:42 2011 +0000
> > +++ b/tools/libxc/xc_private.c  Wed Jan 26 10:46:01 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 e4e69622dc95 -r 8b8b7e024f9d tools/libxc/xc_private.h
> > --- a/tools/libxc/xc_private.h  Wed Jan 26 10:22:42 2011 +0000
> > +++ b/tools/libxc/xc_private.h  Wed Jan 26 10:46:01 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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