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SubjectRe: [PATCH v15 04/13] task_isolation: add initial support
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On 8/29/2016 12:48 PM, Peter Zijlstra wrote:
> On Mon, Aug 29, 2016 at 12:40:32PM -0400, Chris Metcalf wrote:
>> On 8/29/2016 12:33 PM, Peter Zijlstra wrote:
>>> On Tue, Aug 16, 2016 at 05:19:27PM -0400, Chris Metcalf wrote:
>>>> + /*
>>>> + * Request rescheduling unless we are in full dynticks mode.
>>>> + * We would eventually get pre-empted without this, and if
>>>> + * there's another task waiting, it would run; but by
>>>> + * explicitly requesting the reschedule, we may reduce the
>>>> + * latency. We could directly call schedule() here as well,
>>>> + * but since our caller is the standard place where schedule()
>>>> + * is called, we defer to the caller.
>>>> + *
>>>> + * A more substantive approach here would be to use a struct
>>>> + * completion here explicitly, and complete it when we shut
>>>> + * down dynticks, but since we presumably have nothing better
>>>> + * to do on this core anyway, just spinning seems plausible.
>>>> + */
>>>> + if (!tick_nohz_tick_stopped())
>>>> + set_tsk_need_resched(current);
>>> This is broken.. and it would be really good if you don't actually need
>>> to do this.
>> Can you elaborate?
> Naked use of TIF_NEED_RESCHED like this is busted. There is more state
> that needs to be poked to keep things consistent / working.

Would it be cleaner to just replace the set_tsk_need_resched() call
with something like:

set_current_state(TASK_INTERRUPTIBLE);
schedule();
__set_current_state(TASK_RUNNING);

or what would you recommend?

Or, as I said, just doing a busy loop here while testing to see
if need_resched or signal had been set?

--
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com

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