From mboxrd@z Thu Jan 1 00:00:00 1970 From: Manish Awasthi Subject: Re: md raid performance with 3-18-rc3 Date: Tue, 9 Dec 2014 13:54:34 +0530 Message-ID: <5486B1C2.1000508@caviumnetworks.com> References: <5472E7DE.5070702@caviumnetworks.com> <20141125133742.0154a4d4@notabene.brown> <54758B3B.5080907@caviumnetworks.com> <20141203172101.17859aee@notabene.brown> <5486B15C.8060109@caviumnetworks.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5486B15C.8060109@caviumnetworks.com> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids resending: dirty_ratio same for both the kernels. > > vm.dirty_background_bytes = 0 > vm.dirty_background_ratio = 10 > vm.dirty_bytes = 0 > vm.dirty_expire_centisecs = 3000 > vm.dirty_ratio = 20 > vm.dirty_writeback_centisecs = 500 > > > I re-ran the tests with the same set of kernel without enabling > multithread support on 3.18 and measured a few things with perf. > > perf-stat-.txt: test ran for some time and measured various > parameters. > > Meanwhile I'm also running complete test under perf record. I'll share > the results soon. > > Manish > > On 12/03/2014 11:51 AM, NeilBrown wrote: >> On Wed, 26 Nov 2014 13:41:39 +0530 Manish Awasthi >> wrote: >> >>> Whatever data I have on comparison is attached, I have consolidated this >>> 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 files. >> 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 both >> 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 caused >> by other parts of the kernel (filesystem, block layer, MM, etc). Then we can >> 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 >