Messages in this thread | | | Date | Mon, 28 Sep 2015 12:08:17 -0400 | Subject | Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug() | From | Linus Torvalds <> |
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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.
Linus
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