From: Mikulas Patocka <mpatocka@redhat.com> To: Kent Overstreet <koverstreet@google.com> Cc: Vivek Goyal <vgoyal@redhat.com>, linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, tj@kernel.org, bharrosh@panasas.com, Jens Axboe <axboe@kernel.dk> Subject: Re: [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers Date: Mon, 3 Sep 2012 16:41:37 -0400 (EDT) [thread overview] Message-ID: <Pine.LNX.4.64.1209031638110.15620@file.rdu.redhat.com> (raw) In-Reply-To: <20120831014359.GB15218@moria.home.lan> On Thu, 30 Aug 2012, Kent Overstreet wrote: > On Thu, Aug 30, 2012 at 06:07:45PM -0400, Vivek Goyal wrote: > > On Wed, Aug 29, 2012 at 10:13:45AM -0700, Kent Overstreet wrote: > > > > [..] > > > > Performance aside, punting submission to per device worker in case of deep > > > > stack usage sounds cleaner solution to me. > > > > > > Agreed, but performance tends to matter in the real world. And either > > > way the tricky bits are going to be confined to a few functions, so I > > > don't think it matters that much. > > > > > > If someone wants to code up the workqueue version and test it, they're > > > more than welcome... > > > > Here is one quick and dirty proof of concept patch. It checks for stack > > depth and if remaining space is less than 20% of stack size, then it > > defers the bio submission to per queue worker. > > I can't think of any correctness issues. I see some stuff that could be > simplified (blk_drain_deferred_bios() is redundant, just make it a > wrapper around blk_deffered_bio_work()). > > Still skeptical about the performance impact, though - frankly, on some > of the hardware I've been running bcache on this would be a visible > performance regression - probably double digit percentages but I'd have > to benchmark it. That kind of of hardware/usage is not normal today, > but I've put a lot of work into performance and I don't want to make > things worse without good reason. > > Have you tested/benchmarked it? > > There's scheduling behaviour, too. We really want the workqueue thread's > cpu time to be charged to the process that submitted the bio. (We could > use a mechanism like that in other places, too... not like this is a new > issue). > > This is going to be a real issue for users that need strong isolation - > for any driver that uses non negligable cpu (i.e. dm crypt), we're > breaking that (not that it wasn't broken already, but this makes it > worse). ... or another possibility - start a timer when something is put to current->bio_list and use that timer to pop entries off current->bio_list and submit them to a workqueue. The timer can be cpu-local so only interrupt masking is required to synchronize against the timer. This would normally run just like the current kernel and in case of deadlock, the timer would kick in and resolve the deadlock. > I could be convinced, but right now I prefer my solution. It fixes bio allocation problem, but not other similar mempool problems in dm and md. Mikulas
WARNING: multiple messages have this Message-ID (diff)
From: Mikulas Patocka <mpatocka-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> To: Kent Overstreet <koverstreet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> Cc: Vivek Goyal <vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, bharrosh-C4P08NqkoRlBDgjK7y7TUQ@public.gmane.org, Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> Subject: Re: [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers Date: Mon, 3 Sep 2012 16:41:37 -0400 (EDT) [thread overview] Message-ID: <Pine.LNX.4.64.1209031638110.15620@file.rdu.redhat.com> (raw) In-Reply-To: <20120831014359.GB15218-jC9Py7bek1znysI04z7BkA@public.gmane.org> On Thu, 30 Aug 2012, Kent Overstreet wrote: > On Thu, Aug 30, 2012 at 06:07:45PM -0400, Vivek Goyal wrote: > > On Wed, Aug 29, 2012 at 10:13:45AM -0700, Kent Overstreet wrote: > > > > [..] > > > > Performance aside, punting submission to per device worker in case of deep > > > > stack usage sounds cleaner solution to me. > > > > > > Agreed, but performance tends to matter in the real world. And either > > > way the tricky bits are going to be confined to a few functions, so I > > > don't think it matters that much. > > > > > > If someone wants to code up the workqueue version and test it, they're > > > more than welcome... > > > > Here is one quick and dirty proof of concept patch. It checks for stack > > depth and if remaining space is less than 20% of stack size, then it > > defers the bio submission to per queue worker. > > I can't think of any correctness issues. I see some stuff that could be > simplified (blk_drain_deferred_bios() is redundant, just make it a > wrapper around blk_deffered_bio_work()). > > Still skeptical about the performance impact, though - frankly, on some > of the hardware I've been running bcache on this would be a visible > performance regression - probably double digit percentages but I'd have > to benchmark it. That kind of of hardware/usage is not normal today, > but I've put a lot of work into performance and I don't want to make > things worse without good reason. > > Have you tested/benchmarked it? > > There's scheduling behaviour, too. We really want the workqueue thread's > cpu time to be charged to the process that submitted the bio. (We could > use a mechanism like that in other places, too... not like this is a new > issue). > > This is going to be a real issue for users that need strong isolation - > for any driver that uses non negligable cpu (i.e. dm crypt), we're > breaking that (not that it wasn't broken already, but this makes it > worse). ... or another possibility - start a timer when something is put to current->bio_list and use that timer to pop entries off current->bio_list and submit them to a workqueue. The timer can be cpu-local so only interrupt masking is required to synchronize against the timer. This would normally run just like the current kernel and in case of deadlock, the timer would kick in and resolve the deadlock. > I could be convinced, but right now I prefer my solution. It fixes bio allocation problem, but not other similar mempool problems in dm and md. Mikulas
next prev parent reply other threads:[~2012-09-03 20:41 UTC|newest] Thread overview: 128+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-08-28 17:37 [PATCH v7 0/9] Block cleanups, deadlock fix Kent Overstreet 2012-08-28 17:37 ` [PATCH v7 1/9] block: Generalized bio pool freeing Kent Overstreet 2012-08-28 17:37 ` Kent Overstreet 2012-08-28 17:37 ` [PATCH v7 2/9] dm: Use bioset's front_pad for dm_rq_clone_bio_info Kent Overstreet 2012-08-28 17:37 ` [PATCH v7 3/9] block: Add bio_reset() Kent Overstreet 2012-08-28 17:37 ` Kent Overstreet 2012-08-28 20:31 ` Tejun Heo 2012-08-28 20:31 ` Tejun Heo 2012-08-28 22:17 ` Kent Overstreet 2012-08-28 22:53 ` Kent Overstreet 2012-08-28 22:53 ` Kent Overstreet 2012-09-01 2:23 ` Tejun Heo 2012-09-01 2:23 ` Tejun Heo 2012-09-05 20:13 ` Kent Overstreet 2012-08-28 17:37 ` [PATCH v7 4/9] pktcdvd: Switch to bio_kmalloc() Kent Overstreet 2012-08-28 20:32 ` Tejun Heo 2012-08-28 20:32 ` Tejun Heo 2012-08-28 22:24 ` Kent Overstreet 2012-09-04 9:05 ` Jiri Kosina 2012-09-04 9:05 ` Jiri Kosina 2012-09-05 19:44 ` Kent Overstreet 2012-09-05 19:44 ` Kent Overstreet 2012-08-28 17:37 ` [PATCH v7 5/9] block: Kill bi_destructor Kent Overstreet 2012-08-28 20:36 ` Tejun Heo 2012-08-28 20:36 ` Tejun Heo 2012-08-28 22:07 ` Kent Overstreet 2012-08-28 17:37 ` [PATCH v7 6/9] block: Consolidate bio_alloc_bioset(), bio_kmalloc() Kent Overstreet 2012-08-28 17:37 ` Kent Overstreet 2012-08-28 20:41 ` Tejun Heo 2012-08-28 20:41 ` Tejun Heo 2012-08-28 22:03 ` Kent Overstreet 2012-08-28 22:03 ` Kent Overstreet 2012-09-01 2:17 ` Tejun Heo 2012-08-28 17:37 ` [PATCH v7 7/9] block: Add bio_clone_bioset(), bio_clone_kmalloc() Kent Overstreet 2012-08-28 20:44 ` Tejun Heo 2012-08-28 20:44 ` Tejun Heo 2012-08-28 22:05 ` Kent Overstreet 2012-09-01 2:19 ` Tejun Heo 2012-09-01 2:19 ` Tejun Heo 2012-08-28 17:37 ` [PATCH v7 8/9] block: Reorder struct bio_set Kent Overstreet 2012-08-28 17:37 ` [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers Kent Overstreet 2012-08-28 20:49 ` Tejun Heo 2012-08-28 20:49 ` Tejun Heo 2012-08-28 22:28 ` Kent Overstreet 2012-08-28 23:01 ` Kent Overstreet 2012-08-28 23:01 ` Kent Overstreet 2012-08-29 1:31 ` Vivek Goyal 2012-08-29 1:31 ` Vivek Goyal 2012-08-29 3:25 ` Kent Overstreet 2012-08-29 12:57 ` Vivek Goyal 2012-08-29 12:57 ` Vivek Goyal 2012-08-29 14:39 ` [dm-devel] " Alasdair G Kergon 2012-08-29 14:39 ` Alasdair G Kergon 2012-08-29 16:26 ` Kent Overstreet 2012-08-29 16:26 ` Kent Overstreet 2012-08-29 21:01 ` John Stoffel 2012-08-29 21:08 ` Kent Overstreet 2012-08-29 21:08 ` Kent Overstreet 2012-08-28 22:06 ` Vivek Goyal 2012-08-28 22:06 ` Vivek Goyal 2012-08-28 22:23 ` Kent Overstreet 2012-08-28 22:23 ` Kent Overstreet 2012-08-29 16:24 ` Mikulas Patocka 2012-08-29 16:50 ` Kent Overstreet 2012-08-29 16:57 ` [dm-devel] " Alasdair G Kergon 2012-08-29 16:57 ` Alasdair G Kergon 2012-08-29 17:07 ` Vivek Goyal 2012-08-29 17:07 ` Vivek Goyal 2012-08-29 17:13 ` Kent Overstreet 2012-08-29 17:13 ` Kent Overstreet 2012-08-29 17:23 ` [dm-devel] " Alasdair G Kergon 2012-08-29 17:23 ` Alasdair G Kergon 2012-08-29 17:32 ` Kent Overstreet 2012-08-30 22:07 ` Vivek Goyal 2012-08-30 22:07 ` Vivek Goyal 2012-08-31 1:43 ` Kent Overstreet 2012-08-31 1:43 ` Kent Overstreet 2012-08-31 1:55 ` Kent Overstreet 2012-08-31 1:55 ` Kent Overstreet 2012-08-31 15:01 ` Vivek Goyal 2012-09-03 1:26 ` Kent Overstreet 2012-09-03 1:26 ` Kent Overstreet 2012-09-03 20:41 ` Mikulas Patocka [this message] 2012-09-03 20:41 ` Mikulas Patocka 2012-09-04 3:41 ` Kent Overstreet 2012-09-04 3:41 ` Kent Overstreet 2012-09-04 18:55 ` Tejun Heo 2012-09-04 18:55 ` Tejun Heo 2012-09-04 19:01 ` Tejun Heo 2012-09-04 19:43 ` Kent Overstreet 2012-09-04 19:43 ` Kent Overstreet 2012-09-04 19:42 ` Kent Overstreet 2012-09-04 21:03 ` Tejun Heo 2012-09-04 21:03 ` Tejun Heo 2012-09-04 19:26 ` Mikulas Patocka 2012-09-04 19:26 ` Mikulas Patocka 2012-09-04 19:39 ` Vivek Goyal 2012-09-04 19:39 ` Vivek Goyal 2012-09-04 19:51 ` [PATCH] dm: Use bioset's front_pad for dm_target_io Kent Overstreet 2012-09-04 19:51 ` Kent Overstreet 2012-09-04 21:20 ` Tejun Heo 2012-09-04 21:20 ` Tejun Heo 2012-09-11 19:28 ` [PATCH 2] " Mikulas Patocka 2012-09-11 19:28 ` Mikulas Patocka 2012-09-11 19:50 ` Kent Overstreet 2012-09-11 19:50 ` Kent Overstreet 2012-09-12 22:31 ` Mikulas Patocka 2012-09-12 22:31 ` Mikulas Patocka 2012-09-14 23:09 ` [dm-devel] " Alasdair G Kergon 2012-09-14 23:09 ` Alasdair G Kergon 2012-09-01 2:13 ` [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers Tejun Heo 2012-09-01 2:13 ` Tejun Heo 2012-09-03 1:34 ` [PATCH v2] " Kent Overstreet 2012-09-03 1:34 ` Kent Overstreet 2012-09-04 15:00 ` [PATCH v7 9/9] " Vivek Goyal 2012-09-04 15:00 ` Vivek Goyal 2012-09-03 0:49 ` Dave Chinner 2012-09-03 0:49 ` Dave Chinner 2012-09-03 1:17 ` Kent Overstreet 2012-09-03 1:17 ` Kent Overstreet 2012-09-04 13:54 ` Vivek Goyal 2012-09-04 13:54 ` Vivek Goyal 2012-09-04 18:26 ` Tejun Heo 2012-09-04 18:26 ` Tejun Heo 2012-09-05 3:57 ` Dave Chinner 2012-09-05 3:57 ` Dave Chinner 2012-09-05 4:37 ` Tejun Heo 2012-09-05 4:37 ` Tejun Heo
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