From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: RAID5 XOR speed vs RAID6 Q speed (was Re: AVX RAID5 xor checksumming) Date: Sat, 31 Mar 2012 12:38:56 +0100 Message-ID: <4F76ECD0.1060608@anonymous.org.uk> References: <1333057458-2986-1-git-send-email-james.t.kukunas@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1333057458-2986-1-git-send-email-james.t.kukunas@linux.intel.com> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 29/03/2012 22:44, Jim Kukunas wrote: > Based on xor_speed, the AVX implementation appears to be ~32% faster than the > SSE implementation on my i7 2600: > > generic_sse: 15088.000 MB/sec > avx: 19936.000 MB/sec I just noticed in my logs the other day (recent el5 kernel on a Core 2): raid5: automatically using best checksumming function: generic_sse generic_sse: 7805.000 MB/sec raid5: using function: generic_sse (7805.000 MB/sec) raid6: int64x1 2635 MB/s raid6: int64x2 3208 MB/s raid6: int64x4 3020 MB/s raid6: int64x8 2519 MB/s raid6: sse2x1 5099 MB/s raid6: sse2x2 5742 MB/s raid6: sse2x4 8237 MB/s raid6: using algorithm sse2x4 (8237 MB/s) I was just wondering how it's possible to do the RAID6 Q calculation faster than the RAID5 XOR calculation - or am I reading this log excerpt wrongly? It's probably academic, since the machine this is running on only has a maximum of about 4500 MB/s of memory throughput, and a lot of that would be consumed sending data to disc in amongst the calculations being done. Cheers, John.