From: Benjamin LaHaise <bcrl@linux.intel.com>
To: akpm@osdl.org
Cc: linux-mm@kvack.org
Subject: [PATCH] use 32 bit division in slab_put_obj()
Date: Fri, 20 Jan 2006 17:12:46 -0800 [thread overview]
Message-ID: <20060121011245.GA24301@linux.intel.com> (raw)
The patch below improves the performance of slab_put_obj(). Without the
cast, gcc considers ptrdiff_t a 64 bit signed integer and ends up emitting
code to use a full signed 128 bit divide on EM64T, which is substantially
slower than a 32 bit unsigned divide. I noticed this when looking at the
profile of a case where the slab balance is just on edge and thrashes back
and forth freeing a block.
Signed-off-by: Benjamin LaHaise <benjamin.c.lahaise@intel.com>
diff -X work-2.6.16-rc1-mm2/Documentation/dontdiff -urP /home/bcrl/kernels/v2.6/linux-2.6.16-rc1-mm2/mm/slab.c work-2.6.16-rc1-mm2/mm/slab.c
--- /home/bcrl/kernels/v2.6/linux-2.6.16-rc1-mm2/mm/slab.c 2006-01-20 15:20:16.000000000 -0500
+++ work-2.6.16-rc1-mm2/mm/slab.c 2006-01-20 16:41:59.000000000 -0500
@@ -2267,8 +2267,12 @@
static void slab_put_obj(struct kmem_cache *cachep, struct slab *slabp, void *objp,
int nodeid)
{
- unsigned int objnr = (objp - slabp->s_mem) / cachep->buffer_size;
+ /* Slabs are always <4GB in size, so use a less expensive division. */
+ unsigned objnr = (unsigned)(objp - slabp->s_mem) / cachep->buffer_size;
+#if DEBUG
+ WARN_ON((unsigned long)(objp - slabp->s_mem) > ~0U);
+#endif
#if 0
/* Verify that the slab belongs to the intended node */
WARN_ON(slabp->nodeid != nodeid);
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next reply other threads:[~2006-01-21 1:12 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-21 1:12 Benjamin LaHaise [this message]
2006-01-23 6:39 ` [PATCH] use 32 bit division in slab_put_obj() Andrew Morton
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20060121011245.GA24301@linux.intel.com \
--to=bcrl@linux.intel.com \
--cc=akpm@osdl.org \
--cc=linux-mm@kvack.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.