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Subject: Re: [PATCH 2/3 v2] Optimize CRC32C calculation with PCLMULQDQ
 instruction
From: Tim Chen <tim.c.chen@linux.intel.com>
To: Herbert Xu <herbert@gondor.hengli.com.au>
Cc: "H. Peter Anvin" <hpa@zytor.com>, "David S. Miller" <davem@davemloft.net>,
        Suresh Siddha <suresh.b.siddha@intel.com>,
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        James Guilford <james.guilford@intel.com>,
        Wajdi Feghali <wajdi.k.feghali@intel.com>, Min Li <min.a.li@intel.com>,
        David Cote <david.m.cote@intel.com>,
        Fengguang Wu <fengguang.wu@intel.com>
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Date: Tue, 26 Feb 2013 08:57:41 -0800
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On Tue, 2013-02-26 at 17:54 +0800, Herbert Xu wrote:
> On Thu, Sep 27, 2012 at 03:44:22PM -0700, Tim Chen wrote:
> > This patch adds the crc_pcl function that calculates CRC32C checksum using the
> > PCLMULQDQ instruction on processors that support this feature. This will
> > provide speedup over using CRC32 instruction only.
> > The usage of PCLMULQDQ necessitate the invocation of kernel_fpu_begin and
> > kernel_fpu_end and incur some overhead.  So the new crc_pcl function is only
> > invoked for buffer size of 512 bytes or more.  Larger sized
> > buffers will expect to see greater speedup.  This feature is best used coupled
> > with eager_fpu which reduces the kernel_fpu_begin/end overhead.  For
> > buffer size of 1K the speedup is around 1.6x and for buffer size greater than
> > 4K, the speedup is around 3x compared to original implementation in crc32c-intel
> > module. Test was performed on Sandy Bridge based platform with constant frequency
> > set for cpu.
> > 
> > A white paper detailing the algorithm can be found here:
> > http://download.intel.com/design/intarch/papers/323405.pdf
> > 
> > Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>

Acked.  

BTW, Herbert, I've also sent you a patch a few days ago to update the
link to the whitepaper on the CRC32C algorithm in the code.  Wonder if
you have received it.  Thanks.

Tim