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Date: Tue, 18 May 2010 18:37:42 +0200
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Subject: Re: [Qemu-devel] [PATCH] virtio-blk: Avoid zeroing every request
	structure
From: Corentin Chary <corentin.chary@gmail.com>
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To: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Cc: qemu-devel@nongnu.org

On Fri, May 14, 2010 at 11:52 PM, Stefan Hajnoczi
<stefanha@linux.vnet.ibm.com> wrote:
> The VirtIOBlockRequest structure is about 40 KB in size. =A0This patch
> avoids zeroing every request by only initializing fields that are read.
> The other fields are either written to or may not be used at all.
>
> Oprofile shows about 10% of CPU samples in memset called by
> virtio_blk_alloc_request(). =A0The workload is
> dd if=3D/dev/vda of=3D/dev/null iflag=3Ddirect bs=3D8k running concurrent=
ly 4
> times. =A0This patch makes memset disappear to the bottom of the profile.
>

Did you try to profile using calloc in qemu_mallocz instead of malloc + mem=
set ?

$ man calloc
calloc()  allocates memory for an array of nmemb elements of size
bytes each and returns a pointer to the allocated memory.  __The
memory is set to zero.__

--=20
Corentin Chary
http://xf.iksaif.net