Thread (3 messages) 3 messages, 3 authors, 2012-05-03

Re: [PATCH] arch/x86: use kernel_fpu_[begin|end] for RAID5 checksumming

From: "H. Peter Anvin" <hpa@zytor.com>
Date: 2012-05-03 06:43:47
Also in: lkml

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On 05/02/2012 09:57 PM, NeilBrown wrote:
On Mon, 30 Apr 2012 16:51:15 -0700 Jim Kukunas 
[off-list ref] wrote:
quoted
Currently, the SSE and AVX xor functions manually save and 
restore the [X|Y]MM registers. Instead, we should use 
kernel_fpu_[begin|end].

This patch sacrifices some throughput,~5-10% for AVX and ~2% for 
SSE, in exchange for safety against future FPU corruption bugs.

Patch applies to md/for-next.

Signed-off-by: Jim Kukunas <redacted>
Hi Jim, I'm really not able to assess the validity of this patch.
I don't doubt it exactly, but I'd value a second opinion just to
be confident. Peter: can you review and comment?

Thanks, NeilBrown
Are these functions ever called with unaligned arguments?

Other than that, the patch is correct, and is the preferred way to do
this, but I'm unhappy about the cost.  I have suggested to Jim a few
ways by which we might be able to mitigate the cost or even improve
performance, but the implementation depends very much on the above
question (unlike the RAID-6 code, which assumes aligned buffers at all
times.)

	-hpa
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