From: Thomas Monjalon <thomas.monjalon@6wind.com>
To: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH] hash: reverse the operand order to crc32 in rte_hash_crc.h
Date: Tue, 25 Feb 2014 11:57:51 +0100 [thread overview]
Message-ID: <201402251157.51697.thomas.monjalon@6wind.com> (raw)
In-Reply-To: <1393322860-26310-1-git-send-email-hpa@zytor.com>
25/02/2014 11:07, H. Peter Anvin:
> From: "H. Peter Anvin" <hpa@linux.intel.com>
>
> Checkin
>
> a132a9cf2bcd440a974b9d3f5c44ba30b2c895a1 hash: use intrinsic
>
> changed the rte_hash_crc.h from using the crc32 instruction via inline
> assembly to using an intrinsic. The intrinsic should allow for better
> compiler performance, but the change did not account for the fact that
> the inline assembly being in AT&T syntax used the opposite operand
> order of the intrinsic.
>
> This turns out to not matter for correctness, because the CRC32
> operation is commutative. However, it could potentially matter for
> performance, because the loop is more efficient with the moving
> pointer in the source operand and the accumulation in the destination
> operand.
>
> This was discovered by Jan Beulich when looking at the equivalent code
> in the Linux kernel.
>
> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
It was also reported by Pashupati Kumar <kumarp@brocade.com>.
Acked and applied.
Thanks
--
Thomas
prev parent reply other threads:[~2014-02-25 10:56 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-25 10:07 H. Peter Anvin
2014-02-25 10:57 ` Thomas Monjalon [this message]
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