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Re: [PATCH] task_work: remove fifo ordering guarantee

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On 08/28, Eric Dumazet wrote:
>
> From: Eric Dumazet <edumazet@google.com>
>
> In commit f341861fb0b ("task_work: add a scheduling point in
> task_work_run()") I fixed a latency problem adding a cond_resched()
> call.
>
> Later, commit ac3d0da8f329 added yet another loop to reverse a list,
> bringing back the latency spike :
>
> I've seen in some cases this loop taking 275 ms, if for example a
> process with 2,000,000 files is killed.
>
> We could add yet another cond_resched() in the reverse loop,

Can't we do this?

> or we
> can simply remove the reversal, as I do not think anything
> would depend on order of task_work_add() submitted works.

Personally I'd prefer to keep the fifo ordering. It just makes
more sense imho. Even if currently nobody depends on it (although
I am not sure about out-of-tree modules, say, systemtap).

Let's look keyctl_session_to_parent(). It does task_work_cancel()
but only because we can not trust user-space. Otherwise we could
remove it and just do task_work_add(), but this needs fifo.

Fifo just looks more sane to me.

Oleg.

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[PATCH] task_work: remove fifo ordering guarantee Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-29 04:50 +0200
  Re: [PATCH] task_work: remove fifo ordering guarantee Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-29 05:20 +0200
    Re: [PATCH] task_work: remove fifo ordering guarantee Ingo Molnar <mingo@kernel.org> - 2015-08-29 11:30 +0200
      Re: [PATCH] task_work: remove fifo ordering guarantee Oleg Nesterov <oleg@redhat.com> - 2015-08-29 15:00 +0200
        Re: [PATCH] task_work: remove fifo ordering guarantee Ingo Molnar <mingo@kernel.org> - 2015-08-31 08:10 +0200
          Re: [PATCH] task_work: remove fifo ordering guarantee Oleg Nesterov <oleg@redhat.com> - 2015-08-31 15:00 +0200
  Re: [PATCH] task_work: remove fifo ordering guarantee Oleg Nesterov <oleg@redhat.com> - 2015-08-29 15:00 +0200
    Re: [PATCH] task_work: remove fifo ordering guarantee Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-29 16:00 +0200
      Re: [PATCH] task_work: remove fifo ordering guarantee Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-29 16:20 +0200
        Re: [PATCH] task_work: remove fifo ordering guarantee Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-29 19:10 +0200
          Re: [PATCH] task_work: remove fifo ordering guarantee yalin wang <yalin.wang2010@gmail.com> - 2015-08-31 07:30 +0200
            Re: [PATCH] task_work: remove fifo ordering guarantee Al Viro <viro@ZenIV.linux.org.uk> - 2015-09-05 07:20 +0200
          Re: [PATCH] task_work: remove fifo ordering guarantee Oleg Nesterov <oleg@redhat.com> - 2015-08-31 14:50 +0200
          Re: [PATCH] task_work: remove fifo ordering guarantee Al Viro <viro@ZenIV.linux.org.uk> - 2015-09-05 07:20 +0200
            Re: [PATCH] task_work: remove fifo ordering guarantee Al Viro <viro@ZenIV.linux.org.uk> - 2015-09-05 07:50 +0200
              Re: [PATCH] task_work: remove fifo ordering guarantee Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-05 22:50 +0200
      change filp_close() to use __fput_sync() ? (Was: [PATCH]  task_work: remove fifo ordering guarantee) Oleg Nesterov <oleg@redhat.com> - 2015-08-31 14:10 +0200
    Re: [PATCH] task_work: remove fifo ordering guarantee Al Viro <viro@ZenIV.linux.org.uk> - 2015-09-05 07:40 +0200

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