Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug()

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug()
Date	2015-09-29 10:00 +0200
Message-ID	<qdXZo-ds-11@gated-at.bofh.it> (permalink)
References	(5 earlier) <qa5Vx-6Jf-59@gated-at.bofh.it> <qa6oy-7wu-29@gated-at.bofh.it> <qa6ye-7HP-33@gated-at.bofh.it> <qdHUB-2nN-7@gated-at.bofh.it> <qdJa1-4l8-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Mon, Sep 28, 2015 at 10:47 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> >> It gets set by preemption - and,
> >> somewhat illogically, by cond_resched().
> >
> > I suspect that was done to make cond_resched() (voluntary preemption)
> > more robust and only have a single preemption path/logic. But all that
> > was done well before I got involved.
> 
> So I think it's actually the name that is bad, not necessarily the behavior.
> 
> We tend to put "cond_resched()" (and particularly
> "cond_resched_lock()") in some fairly awkward places, and it's not
> always entirely clear that task->state == TASK_RUNNING there.
> 
> So the preemptive behavior of not *really* putting the task to sleep
> may actually be the right one. But it is rather non-intuitive given
> the name - because "cond_resched()" basically is not at all equivalent
> to "if (need_resched()) schedule()", which you'd kind of expect.
> 
> An explicit schedule will actually act on the task->state, and make us
> go to sleep. "cond_resched()"  really is just a "voluntary preemption
> point". And I think it would be better if it got named that way.

cond_preempt() perhaps? That would allude to preempt_schedule() and such, and 
would make it clearer that it's supposed to be an invariant on the sleep state 
(which schedule() is not).

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug() Peter Zijlstra <peterz@infradead.org> - 2015-09-28 16:50 +0200
  Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug() Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-28 18:10 +0200
    Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug() Ingo Molnar <mingo@kernel.org> - 2015-09-29 10:00 +0200

csiph-web