Messages in this thread | | | Date | Thu, 17 Sep 2015 12:14:53 +1000 | From | Dave Chinner <> | Subject | Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug() |
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On Wed, Sep 16, 2015 at 06:12:29PM -0700, Linus Torvalds wrote: > On Wed, Sep 16, 2015 at 5:37 PM, Dave Chinner <david@fromorbit.com> wrote: > > > > TL;DR: Results look really bad - not only is the plugging > > problematic, baseline writeback performance has regressed > > significantly. > > Dave, if you're testing my current -git, the other performance issue > might still be the spinlock thing.
I have the fix as the first commit in my local tree - it'll remain there until I get a conflict after an update. :)
> The plugging IO pauses are interesting, though. Plugging really > *shouldn't* cause that kind of pauses, _regardless_ of what level it > happens on, so I wonder if the patch ends up just exposing some really > basic problem that just normally goes hidden.
Right, that's what I suspect - it didn't happen on older kernels, but we've just completely reworked the writeback code for the control group awareness since I last looked really closely at this...
> Can you match up the IO wait times with just *where* it is > waiting? Is it waiting for that inode I_SYNC thing in > inode_sleep_on_writeback()?
I'll do some more investigation.
> But it does sound like we should just revert the whole plugging for > now, if only because "it has odd effects".
Yup - we can add it again next merge window once we get to the bottom of whatever is going on and have had time to test the new code properly.
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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