From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: Revert "dm: always call blk_queue_split() in dm_process_bio()" Date: Tue, 15 Sep 2020 13:03:33 -0400 Message-ID: <20200915170333.GA20998@redhat.com> References: <529c2394-1b58-b9d8-d462-1f3de1b78ac8@oracle.com> <20200910142438.GA21919@redhat.com> <5261af10-bf5c-f768-dbeb-2e784a5823f9@oracle.com> <20200915013308.GA14877@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20200915013308.GA14877@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com Content-Disposition: inline To: Vijayendra Suman Cc: linux-block@vger.kernel.org, Somu Krishnasamy , dm-devel@redhat.com, RAMANAN_GOVINDARAJAN List-Id: dm-devel.ids On Mon, Sep 14 2020 at 9:33pm -0400, Mike Snitzer wrote: > On Thu, Sep 10 2020 at 3:29pm -0400, > Vijayendra Suman wrote: > > > Hello Mike, > > > > I checked with upstream, performance measurement is similar and > > shows performance improvement when > > 120c9257f5f19e5d1e87efcbb5531b7cd81b7d74 is reverted. > > > > On 9/10/2020 7:54 PM, Mike Snitzer wrote: > > >[cc'ing dm-devel and linux-block because this is upstream concern too] > > > > > >On Wed, Sep 09 2020 at 1:00pm -0400, > > >Vijayendra Suman wrote: > > > > > >> Hello Mike, > > >> > > >> While Running pgbench tool with 5.4.17 kernel build > > >> > > >> Following performance degrade is found out > > >> > > >> buffer read/write metric : -17.2% > > >> cache read/write metric : -18.7% > > >> disk read/write metric : -19% > > >> > > >> buffer > > >> number of transactions actually processed: 840972 > > >> latency average = 24.013 ms > > >> tps = 4664.153934 (including connections establishing) > > >> tps = 4664.421492 (excluding connections establishing) > > >> > > >> cache > > >> number of transactions actually processed: 551345 > > >> latency average = 36.949 ms > > >> tps = 3031.223905 (including connections establishing) > > >> tps = 3031.402581 (excluding connections establishing) > > >> > > >> After revert of Commit > > >> 2892100bc85ae446088cebe0c00ba9b194c0ac9d ( Revert "dm: always call > > >> blk_queue_split() in dm_process_bio()") > > > > > >I assume 2892100bc85ae446088cebe0c00ba9b194c0ac9d is 5.4-stable's > > >backport of upstream commit 120c9257f5f19e5d1e87efcbb5531b7cd81b7d74 ? > > > > Yes > > > > >> Performance is Counter measurement > > >> > > >> buffer -> > > >> number of transactions actually processed: 1135735 > > >> latency average = 17.799 ms > > >> tps = 6292.586749 (including connections establishing) > > >> tps = 6292.875089 (excluding connections establishing) > > >> > > >> cache -> > > >> number of transactions actually processed: 648177 > > >> latency average = 31.217 ms > > >> tps = 3587.755975 (including connections establishing) > > >> tps = 3587.966359 (excluding connections establishing) > > >> > > >> Following is your commit > > >> > > >> diff --git a/drivers/md/dm.c b/drivers/md/dm.c > > >> index cf71a2277d60..1e6e0c970e19 100644 > > >> --- a/drivers/md/dm.c > > >> +++ b/drivers/md/dm.c > > >> @@ -1760,8 +1760,9 @@ static blk_qc_t dm_process_bio(struct mapped_device > > >> *md, > > >> * won't be imposed. > > >> */ > > >> if (current->bio_list) { > > >> - blk_queue_split(md->queue, &bio); > > >> - if (!is_abnormal_io(bio)) > > >> + if (is_abnormal_io(bio)) > > >> + blk_queue_split(md->queue, &bio); > > >> + else > > >> dm_queue_split(md, ti, &bio); > > >> } > > >> > > >> Could you have a look if it is safe to revert this commit. > > >No, it really isn't a good idea given what was documented in the commit > > >header for commit 120c9257f5f19e5d1e87efcbb5531b7cd81b7d74 -- the > > >excessive splitting is not conducive to performance either. > > > > > >So I think we need to identify _why_ reverting this commit is causing > > >such a performance improvement. Why is calling blk_queue_split() before > > >dm_queue_split() benefiting your pgbench workload? > > > > Let me know if you want to check some patch. > > Hi, > > Could you please test this branch?: > https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-5.10 > (or apply at least the first 4 patches, commit 63f85d97be69^..b6a80963621fa) > > So far I've done various DM regression testing. But I haven't tested > with pgbench or with the misaaligned IO scenario documented in the > header for commit 120c9257f5f19e5d1e87efcbb5531b7cd81b7d74. But I'll > test that scenario tomorrow. Training DM core to set chunk_sectors and always use blk_queue_split resolves the inefficient splitting documented in the header for commit 120c9257f5f19e5d1e87efcbb5531b7cd81b7d74. xfs_io -d -c 'pread -b 2m 224s 4072s' /dev/mapper/stripe_dev before, so with commit 120c9257f5f19e5d1e87efcbb5531b7cd81b7d74: 253,2 5 1 0.000000000 4382 Q R 224 + 2064 [xfs_io] 253,2 5 2 0.000003414 4382 X R 224 / 256 [xfs_io] 253,2 5 3 0.000017838 4382 X R 256 / 512 [xfs_io] 253,2 5 4 0.000019852 4382 X R 512 / 768 [xfs_io] 253,2 5 5 0.000031316 4382 X R 768 / 1024 [xfs_io] 253,2 5 6 0.000034333 4382 X R 1024 / 1280 [xfs_io] 253,2 5 7 0.000037684 4382 X R 1280 / 1536 [xfs_io] 253,2 5 8 0.000041011 4382 X R 1536 / 1792 [xfs_io] 253,2 5 9 0.000043962 4382 X R 1792 / 2048 [xfs_io] 253,2 5 10 0.000074765 4382 Q R 2288 + 2008 [xfs_io] 253,2 5 11 0.000075020 4382 X R 2288 / 2304 [xfs_io] 253,2 5 12 0.000077009 4382 X R 2304 / 2560 [xfs_io] 253,2 5 13 0.000080509 4382 X R 2560 / 2816 [xfs_io] 253,2 5 14 0.000084182 4382 X R 2816 / 3072 [xfs_io] 253,2 5 15 0.000087274 4382 X R 3072 / 3328 [xfs_io] 253,2 5 16 0.000090342 4382 X R 3328 / 3584 [xfs_io] 253,2 5 17 0.000095348 4382 X R 3584 / 3840 [xfs_io] 253,2 5 18 0.000097776 4382 X R 3840 / 4096 [xfs_io] after, so with 'dm-5.10' branch refernced above, meaning dm_process_bio w/ unconditional blk_queue_split (w/ chunk_sectors): 253,2 17 1 0.000000000 2176 Q R 224 + 2280 [xfs_io] 253,2 17 2 0.000001978 2176 X R 224 / 256 [xfs_io] 253,2 17 3 0.000017882 2176 X R 256 / 512 [xfs_io] 253,2 17 4 0.000020406 2176 X R 512 / 768 [xfs_io] 253,2 17 5 0.000031298 2176 X R 768 / 1024 [xfs_io] 253,2 17 6 0.000034654 2176 X R 1024 / 1280 [xfs_io] 253,2 17 7 0.000038474 2176 X R 1280 / 1536 [xfs_io] 253,2 17 8 0.000042299 2176 X R 1536 / 1792 [xfs_io] 253,2 17 9 0.000054088 2176 X R 1792 / 2048 [xfs_io] 253,2 17 10 0.000057884 2176 X R 2048 / 2304 [xfs_io] 253,2 17 11 0.000081358 2176 Q R 2504 + 1792 [xfs_io] 253,2 17 12 0.000081778 2176 X R 2504 / 2560 [xfs_io] 253,2 17 13 0.000083496 2176 X R 2560 / 2816 [xfs_io] 253,2 17 14 0.000085301 2176 X R 2816 / 3072 [xfs_io] 253,2 17 15 0.000092374 2176 X R 3072 / 3328 [xfs_io] 253,2 17 16 0.000094774 2176 X R 3328 / 3584 [xfs_io] 253,2 17 17 0.000097977 2176 X R 3584 / 3840 [xfs_io] 253,2 17 18 0.000100094 2176 X R 3840 / 4096 [xfs_io] > Any chance you could provide some hints on how you're running pgbench > just so I can try to test/reproduce/verify locally? I'm going to defer to you on pgbench testing. What is your underlying storage? Could it be that DM using unconditional blk_queue_split() is helping your pgbench workload because it splits IO more (so smaller IO, lower latency per IO)? Do you have comparison blktrace data? Mike