From: Jeff Moyer <jmoyer@redhat.com>
To: Richard Kennedy <richard@rsk.demon.co.uk>
Cc: Vivek Goyal <vgoyal@redhat.com>,
Jens Axboe <jens.axboe@oracle.com>,
Corrado Zoccolo <czoccolo@gmail.com>,
Gui Jianfeng <guijianfeng@cn.fujitsu.com>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] cfq: reorder cfq_queue removing padding on 64bit & allowing more objects/slab in it's kmem_cache
Date: Mon, 15 Feb 2010 12:01:18 -0500 [thread overview]
Message-ID: <x49eikmph5t.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <1266251188.7362.3.camel@localhost> (Richard Kennedy's message of "Mon, 15 Feb 2010 16:26:28 +0000")
Richard Kennedy <richard@rsk.demon.co.uk> writes:
> This removes 8 bytes of padding from struct cfq_queue on 64 bit builds,
> shrinking it's size to 256 bytes, so fitting into 1 fewer cachelines and
> allowing 1 more object/slab in it's kmem_cache.
OK, I ran pahole to verify your findings:
$ pahole -C cfq_queue build/master/block/cfq-iosched.o
struct cfq_queue {
...
unsigned int allocated_slice; /* 136 4 */
/* XXX 4 bytes hole, try to pack */
long unsigned int slice_start; /* 144 8 */
...
pid_t pid; /* 216 4 */
/* XXX 4 bytes hole, try to pack */
struct cfq_rb_root * service_tree; /* 224 8 */
...
/* size: 264, cachelines: 5, members: 34 */
/* sum members: 256, holes: 2, sum holes: 8 */
/* last cacheline: 8 bytes */
After applying the patch, it indeed does save a cacheline.
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
next prev parent reply other threads:[~2010-02-15 17:01 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-15 14:10 [PATCH] " Richard Kennedy
2010-02-15 14:16 ` Vivek Goyal
2010-02-15 15:32 ` Richard Kennedy
2010-02-15 16:26 ` [PATCH v2] " Richard Kennedy
2010-02-15 17:01 ` Jeff Moyer [this message]
2010-02-22 12:49 ` Jens Axboe
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