On Thu, Dec 29 2016 at 11:08pm -0500, Eric Wheeler <dm-devel@xxxxxxxxxxxxxxxxxx> wrote: > On Sat, 17 Dec 2016, Mike Snitzer wrote: > > On Fri, Dec 16 2016 at 5:29pm -0500, > > Eric Wheeler <dm-devel@xxxxxxxxxxxxxxxxxx> wrote: > > > On Wed, 14 Dec 2016, Eric Wheeler wrote: > > > > Since dm-crypt queues writes (and sometimes reads) to a different kernel > > > > thread (workqueue), the bios will dispatch from tasks with different > > > > io_context->ioprio settings than the submitting task, thus giving > > > > incorrect ioprio hints to the io scheduler. > > > > > > The motivation of this patch is for ioprio-driven writebackup/bypass > > > hinting inside bcache when bcache is under dm-crypt which Jens is picking > > > up for 4.10: > > > https://lkml.org/lkml/2016/12/6/607 > > > > I now see your commits: > > b71de4659fba4e42c7 bcache: introduce per-process ioprio-based bypass/writeback hints > > 82e7192711c3855038 bcache: documentation for ioprio cache hinting > > > > You'd think this is the type of thing that you'd have proposed to a > > wider audience. > > ( Its not really relevant to this bugfix, but please see this thread since > you were curious about a wider audience discussion: > https://www.redhat.com/archives/dm-devel/2016-July/msg00556.html ) > > The note above in the previous email was intended to explain how we > discovered the dm-crypt problem, purely as an example use case. The > stable commit note discusses the real issue: lost elevator hints. > > This commit fixes elevator ioprio hints passing through dm-crypt and is > not intended to address dm-cache, nor enable a bcache feature. > > All impementations using ioprio hints beneath dm-crypt would > benefit---most importantly, _CFQ_ ! > > As it is, all ioprio hints passing through dm-crypt are lost to the > elevator; the elevator looses those useful bits because of queuing to > another thread for crypto operations. How did you test the change? Or put differently: what is the easiest test to run against a dm-crypt device to verify that ioprio is being passed through? -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
