From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: md raid performance with 3-18-rc3 Date: Wed, 3 Dec 2014 17:21:01 +1100 Message-ID: <20141203172101.17859aee@notabene.brown> References: <5472E7DE.5070702@caviumnetworks.com> <20141125133742.0154a4d4@notabene.brown> <54758B3B.5080907@caviumnetworks.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/KBoI2uN/Aho.h0t9zVsdlpo"; protocol="application/pgp-signature" Return-path: In-Reply-To: <54758B3B.5080907@caviumnetworks.com> Sender: linux-raid-owner@vger.kernel.org To: Manish Awasthi Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids --Sig_/KBoI2uN/Aho.h0t9zVsdlpo Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Wed, 26 Nov 2014 13:41:39 +0530 Manish Awasthi wrote: > Whatever data I have on comparison is attached, I have consolidated this= =20 > from log files to excel. See if this helps. raid_3_18_performance.xls shows read throughput to be consistently 20% down on 3.18 compared to 3.6.11. Writes are a few percent better for 4G/8G files, 20% better for 16G/32G fil= es. unchanged above that. Given that you have 8G of RAM, that seems like it could be some change in caching behaviour, and not necessarily a change in RAID behaviour. The CPU utilization roughly follows the throughput: 40% higher when write throughput is 20% better. Could you check if the value of /proc/sys/vm/dirty_ratio is the same for bo= th tests. That number has changed occasionally and could affect these tests. The second file, 3SSDs-perf-2-Cores-3.18-rc1 has the "change" numbers negative where I expected positive.. i.e. negative mean an increase. Writes consistently have higher CPU utilisation. Reads consistently have much lower CPU utilization. I don't know what that means ... it might not mean anything. Could you please run the tests between the two kernels *with* RAID. i.e. directly on an SSD. That will give us a baseline for what changes are caus= ed by other parts of the kernel (filesystem, block layer, MM, etc). Then we c= an see how much change RAID5 is contributing. The third file, 3SSDs-perf-4Core.xls seems to show significantly reduced throughput across the board. CPU utilization is less (better) for writes, but worse for reads. That is the reverse of what the second file shows. I might try running some tests across a set of kernel versions and see what= I can come up with. NeilBrown --Sig_/KBoI2uN/Aho.h0t9zVsdlpo Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIVAwUBVH6rzTnsnt1WYoG5AQK8+A//VGbcQvvYsfATDSZ75cwP8u7tdsY1Xeb5 fAykmtGZojZA8Iq8RC14NA2SzC1CbF05qB6Fgye9lDBP2h+iZWjcJsqXUlWY6uw3 UIc0hbfBAaxyfXeDqt1N/bhLKYJi2PAhy3lxPfSGiHKIz0r9q/eJl+JRwx/z3x/S mqTpUVz8N4OhQLRHqPinD7uEW6iAGg8pE2yKEYTtlY3OTwvymtGFZR1UgvhaBFT5 Pi72ZQy5KZ/wauf7AkQaIjxwNj4SleQJ9dy4rZTvGe8LnQiM8RLQYqqCfKcokZ9q GoTbIXkbuLDaxfNp7n/oE95PtZ/TIPVe116pXhWhzIA+7z2RYD6XD8edCBaNeA9I EunOvrmfIl3CRMyMfDV6TI5xxIOD/vUuW+0nJ0JhTJWMfzL0pSSqGiCzjQn9Zt98 qyapowD7XtcCV0EDYpNg6h9SYgS6gHWUPjW8/MiX490P2iH3+1Zsdnmotm3CC3Ke JET3vQrIMK6OT2WR4TS4XyfnRx3wWrmKmZLX3IkG27QVWTUrnlL7sW0xleClJ343 mc7PJHYkC0jtnhLId1XdD219g+feO51e8WO9+Uj9wS87QdcoJlk5JHWvf2HoIouV VfV4LxnMXN5IQblZMRhvwm7wLYQ6TC4CUGc1VxzJyF7/yXIyEPCltP2Cxtljs8A7 kcByT3q8+zw= =ssBq -----END PGP SIGNATURE----- --Sig_/KBoI2uN/Aho.h0t9zVsdlpo--