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From: Miklos Szeredi <[email protected]>
To: Jens Axboe <[email protected]>
Cc: [email protected]
Subject: Re: io_uring_prep_openat_direct() and link/drain
Date: Thu, 21 Apr 2022 14:31:58 +0200	[thread overview]
Message-ID: <CAJfpegsa8uza8bc1aMD7hLzrD6n1=wbxAmQH2KEOnrw7Rxkz2A@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>

On Tue, 5 Apr 2022 at 16:44, Jens Axboe <[email protected]> wrote:
>
> On 4/5/22 1:45 AM, Miklos Szeredi wrote:
> > On Sat, 2 Apr 2022 at 03:17, Jens Axboe <[email protected]> wrote:
> >>
> >> On 4/1/22 10:21 AM, Jens Axboe wrote:
> >>> On 4/1/22 10:02 AM, Miklos Szeredi wrote:
> >>>> On Fri, 1 Apr 2022 at 17:36, Jens Axboe <[email protected]> wrote:
> >>>>
> >>>>> I take it you're continually reusing those slots?
> >>>>
> >>>> Yes.
> >>>>
> >>>>>  If you have a test
> >>>>> case that'd be ideal. Agree that it sounds like we just need an
> >>>>> appropriate breather to allow fput/task_work to run. Or it could be the
> >>>>> deferral free of the fixed slot.
> >>>>
> >>>> Adding a breather could make the worst case latency be large.  I think
> >>>> doing the fput synchronously would be better in general.
> >>>
> >>> fput() isn't sync, it'll just offload to task_work. There are some
> >>> dependencies there that would need to be checked. But we'll find a way
> >>> to deal with it.
> >>>
> >>>> I test this on an VM with 8G of memory and run the following:
> >>>>
> >>>> ./forkbomb 14 &
> >>>> # wait till 16k processes are forked
> >>>> for i in `seq 1 100`; do ./procreads u; done
> >>>>
> >>>> You can compare performance with plain reads (./procreads p), the
> >>>> other tests don't work on public kernels.
> >>>
> >>> OK, I'll check up on this, but probably won't have time to do so before
> >>> early next week.
> >>
> >> Can you try with this patch? It's not complete yet, there's actually a
> >> bunch of things we can do to improve the direct descriptor case. But
> >> this one is easy enough to pull off, and I think it'll fix your OOM
> >> case. Not a proposed patch, but it'll prove the theory.
> >
> > Sorry for the delay..
> >
> > Patch works like charm.
>
> OK good, then it is the issue I suspected. Thanks for testing!

Tested with v5.18-rc3 and performance seems significantly worse than
with the test patch:

test patch:
        avg     min     max     stdev
real    0.205   0.190   0.266   0.011
user    0.017   0.007   0.029   0.004
sys     0.374   0.336   0.503   0.022

5.18.0-rc3-00016-gb253435746d9:
        avg     min     max     stdev
real    0.725   0.200   18.090  2.279
user    0.019   0.005   0.046   0.006
sys     0.454   0.241   1.022   0.199

Thanks,
Miklos

  reply	other threads:[~2022-04-21 12:32 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-29 13:20 io_uring_prep_openat_direct() and link/drain Miklos Szeredi
2022-03-29 16:08 ` Jens Axboe
2022-03-29 17:04   ` Jens Axboe
2022-03-29 18:21     ` Miklos Szeredi
2022-03-29 18:26       ` Jens Axboe
2022-03-29 18:31         ` Miklos Szeredi
2022-03-29 18:40           ` Jens Axboe
2022-03-29 19:30             ` Miklos Szeredi
2022-03-29 20:03               ` Jens Axboe
2022-03-30  8:18                 ` Miklos Szeredi
2022-03-30 12:35                   ` Jens Axboe
2022-03-30 12:43                     ` Miklos Szeredi
2022-03-30 12:48                       ` Jens Axboe
2022-03-30 12:51                         ` Miklos Szeredi
2022-03-30 14:58                           ` Miklos Szeredi
2022-03-30 15:05                             ` Jens Axboe
2022-03-30 15:12                               ` Miklos Szeredi
2022-03-30 15:17                                 ` Jens Axboe
2022-03-30 15:53                                   ` Jens Axboe
2022-03-30 17:49                                     ` Jens Axboe
2022-04-01  8:40                                       ` Miklos Szeredi
2022-04-01 15:36                                         ` Jens Axboe
2022-04-01 16:02                                           ` Miklos Szeredi
2022-04-01 16:21                                             ` Jens Axboe
2022-04-02  1:17                                               ` Jens Axboe
2022-04-05  7:45                                                 ` Miklos Szeredi
2022-04-05 14:44                                                   ` Jens Axboe
2022-04-21 12:31                                                     ` Miklos Szeredi [this message]
2022-04-21 12:34                                                       ` Jens Axboe
2022-04-21 12:39                                                         ` Miklos Szeredi
2022-04-21 12:41                                                           ` Jens Axboe
2022-04-21 13:10                                                             ` Miklos Szeredi

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