Messages in this thread | | | Date | Tue, 29 Jul 2014 19:31:36 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases |
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On 07/29, Andy Lutomirski wrote: > > On Tue, Jul 29, 2014 at 9:54 AM, Oleg Nesterov <oleg@redhat.com> wrote: > > > > Yes, just to trigger the slow path, I guess. > > > >> I'll update the code to call user_exit iff TIF_NOHZ is > >> set. > > > > Or perhaps it would be better to not add another user of this (strange) flag > > and just call user_exit() unconditionally(). But, yes, you need to use > > from "work = flags & (_TIF_WORK_SYSCALL_ENTRY & ~TIF_NOHZ)" then.\ > > user_exit looks slow enough to me that a branch to try to avoid it may > be worthwhile. I bet that explicitly checking the flag is > actually both faster and clearer.
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.
> That's what I did for v4.
I am going to read it today. Not that I think I can help or find something wrong.
Oleg.
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