Acked-by: Andy Zhou <az...@nicira.com>
On Tue, Mar 11, 2014 at 1:56 PM, Ben Pfaff <b...@nicira.com> wrote:
> This factors code out of fat-rwlock, making it easily usable by other code.
>
> Signed-off-by: Ben Pfaff <b...@nicira.com>
> ---
> lib/fat-rwlock.c | 29 ++------------------------
> lib/util.c | 60
> +++++++++++++++++++++++++++++++++++++++++++++++++++++-
> lib/util.h | 6 +++++-
> 3 files changed, 66 insertions(+), 29 deletions(-)
>
> diff --git a/lib/fat-rwlock.c b/lib/fat-rwlock.c
> index 3866dda..82dfbfe 100644
> --- a/lib/fat-rwlock.c
> +++ b/lib/fat-rwlock.c
> @@ -57,16 +57,6 @@ struct fat_rwlock_slot {
> * Accessed only by the slot's own thread, so no synchronization is
> * needed. */
> unsigned int depth;
> -
> - /* To prevent two of these structures from accidentally occupying the
> same
> - * cache line (causing "false sharing"), we cache-align each of these
> data
> - * structures. That requires malloc()ing extra space and throwing
> away
> - * some space at the beginning, which means that the pointer to this
> struct
> - * isn't necessarily the pointer to the beginning of the block, and
> so we
> - * need to retain the original pointer to free later.
> - *
> - * Accessed only by a single thread, so no synchronization is needed.
> */
> - void *base; /* Pointer to pass to free() for this
> block. */
> };
>
> static void
> @@ -77,7 +67,7 @@ free_slot(struct fat_rwlock_slot *slot)
> }
>
> list_remove(&slot->list_node);
> - free(slot->base);
> + free_cacheline(slot);
> }
>
> static void
> @@ -124,7 +114,6 @@ static struct fat_rwlock_slot *
> fat_rwlock_get_slot__(struct fat_rwlock *rwlock)
> {
> struct fat_rwlock_slot *slot;
> - void *base;
>
> /* Fast path. */
> slot = ovsthread_getspecific(rwlock->key);
> @@ -134,21 +123,7 @@ fat_rwlock_get_slot__(struct fat_rwlock *rwlock)
>
> /* Slow path: create a new slot for 'rwlock' in this thread. */
>
> - /* Allocate room for:
> - *
> - * - Up to CACHE_LINE_SIZE - 1 bytes before the per-thread, so
> that
> - * the start of the slot doesn't potentially share a cache line.
> - *
> - * - The slot itself.
> - *
> - * - Space following the slot up to the end of the cache line, so
> - * that the end of the slot doesn't potentially share a cache
> - * line. */
> - base = xmalloc((CACHE_LINE_SIZE - 1)
> - + ROUND_UP(sizeof *slot, CACHE_LINE_SIZE));
> - slot = (void *) ROUND_UP((uintptr_t) base, CACHE_LINE_SIZE);
> -
> - slot->base = base;
> + slot = xmalloc_cacheline(sizeof *slot);
> slot->rwlock = rwlock;
> ovs_mutex_init(&slot->mutex);
> slot->depth = 0;
> diff --git a/lib/util.c b/lib/util.c
> index 911cc3e..f3a0e41 100644
> --- a/lib/util.c
> +++ b/lib/util.c
> @@ -1,5 +1,5 @@
> /*
> - * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
> + * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014 Nicira, Inc.
> *
> * Licensed under the Apache License, Version 2.0 (the "License");
> * you may not use this file except in compliance with the License.
> @@ -174,6 +174,64 @@ x2nrealloc(void *p, size_t *n, size_t s)
> return xrealloc(p, *n * s);
> }
>
> +/* The desired minimum alignment for an allocated block of memory. */
> +#define MEM_ALIGN MAX(sizeof(void *), 8)
> +BUILD_ASSERT_DECL(IS_POW2(MEM_ALIGN));
> +BUILD_ASSERT_DECL(CACHE_LINE_SIZE >= MEM_ALIGN);
> +
> +/* Allocates and returns 'size' bytes of memory in dedicated cache lines.
> That
> + * is, the memory block returned will not share a cache line with other
> data,
> + * avoiding "false sharing". (The memory returned will not be at the
> start of
> + * a cache line, though, so don't assume such alignment.)
> + *
> + * Use free_cacheline() to free the returned memory block. */
> +void *
> +xmalloc_cacheline(size_t size)
> +{
> + void **payload;
> + void *base;
> +
> + /* Allocate room for:
> + *
> + * - Up to CACHE_LINE_SIZE - 1 bytes before the payload, so that
> the
> + * start of the payload doesn't potentially share a cache line.
> + *
> + * - A payload consisting of a void *, followed by padding out to
> + * MEM_ALIGN bytes, followed by 'size' bytes of user data.
> + *
> + * - Space following the payload up to the end of the cache line,
> so
> + * that the end of the payload doesn't potentially share a
> cache line
> + * with some following block. */
> + base = xmalloc((CACHE_LINE_SIZE - 1)
> + + ROUND_UP(MEM_ALIGN + size, CACHE_LINE_SIZE));
> +
> + /* Locate the payload and store a pointer to the base at the
> beginning. */
> + payload = (void **) ROUND_UP((uintptr_t) base, CACHE_LINE_SIZE);
> + *payload = base;
> +
> + return (char *) payload + MEM_ALIGN;
> +}
> +
> +/* Like xmalloc_cacheline() but clears the allocated memory to all zero
> + * bytes. */
> +void *
> +xzalloc_cacheline(size_t size)
> +{
> + void *p = xmalloc_cacheline(size);
> + memset(p, 0, size);
> + return p;
> +}
> +
> +/* Frees a memory block allocated with xmalloc_cacheline() or
> + * xzalloc_cacheline(). */
> +void
> +free_cacheline(void *p)
> +{
> + if (p) {
> + free(*(void **) ((uintptr_t) p - MEM_ALIGN));
> + }
> +}
> +
> char *
> xasprintf(const char *format, ...)
> {
> diff --git a/lib/util.h b/lib/util.h
> index 64516a8..9f1dc4c 100644
> --- a/lib/util.h
> +++ b/lib/util.h
> @@ -1,5 +1,5 @@
> /*
> - * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
> + * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014 Nicira, Inc.
> *
> * Licensed under the Apache License, Version 2.0 (the "License");
> * you may not use this file except in compliance with the License.
> @@ -264,6 +264,10 @@ char *xasprintf(const char *format, ...)
> PRINTF_FORMAT(1, 2) MALLOC_LIKE;
> char *xvasprintf(const char *format, va_list) PRINTF_FORMAT(1, 0)
> MALLOC_LIKE;
> void *x2nrealloc(void *p, size_t *n, size_t s);
>
> +void *xmalloc_cacheline(size_t) MALLOC_LIKE;
> +void *xzalloc_cacheline(size_t) MALLOC_LIKE;
> +void free_cacheline(void *);
> +
> void ovs_strlcpy(char *dst, const char *src, size_t size);
> void ovs_strzcpy(char *dst, const char *src, size_t size);
>
> --
> 1.7.10.4
>
> _______________________________________________
> dev mailing list
> dev@openvswitch.org
> http://openvswitch.org/mailman/listinfo/dev
>
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