On 07/29, Andy Lutomirski wrote:
>
> On Tue, Jul 29, 2014 at 10:31 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >
> > I don't think so (unless I am confused again), note that user_exit() uses
> > jump label. But this doesn't matter. I meant that we should avoid TIF_NOHZ
> > if possible because I think it should die somehow (currently I do not know
> > how ;). And because it is ugly to check the same condition twice:
> >
> > if (work & TIF_NOHZ) {
> > // user_exit()
> > if (context_tracking_is_enabled())
> > context_tracking_user_exit();
> > }
> >
> > TIF_NOHZ is set if and only if context_tracking_is_enabled() is true.
> > So I think that
> >
> > work = current_thread_info()->flags & (_TIF_WORK_SYSCALL_ENTRY & ~TIF_NOHZ);
> >
> > user_exit();
> >
> > looks a bit better. But I won't argue.
>
> I don't get it.
Don't worry, you are not alone.
> context_tracking_is_enabled is global, and TIF_NOHZ
> is per-task. Isn't this stuff determined per-task or per-cpu or
> something?
>
> IOW, if one CPU is running something that's very heavily
> userspace-oriented and another CPU is doing something syscall- or
> sleep-heavy, then shouldn't only the first CPU end up paying the price
> of context tracking?
Please see another email I sent to Frederic.
Oleg.
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