From: Nicholas Piggin <npiggin@gmail.com>
To: Joel Fernandes <joel.opensrc@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] tracing/irqtrace: only call trace_hardirqs_on/off when state changes
Date: Wed, 2 May 2018 10:12:14 +1000 [thread overview]
Message-ID: <20180502101214.746650bc@roar.ozlabs.ibm.com> (raw)
In-Reply-To: <CAEi0qNkbjrdx8A4rfNCJd-1BGMUXZRbbLJEkZuVab+oprWhcDQ@mail.gmail.com>
On Tue, 1 May 2018 14:15:14 -0700
Joel Fernandes <joel.opensrc@gmail.com> wrote:
> On Tue, May 1, 2018 at 1:00 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Tue, 1 May 2018 21:48:38 +0200
> > Peter Zijlstra <peterz@infradead.org> wrote:
> >
> >> On Tue, May 01, 2018 at 03:38:40PM -0400, Steven Rostedt wrote:
> >> > On Tue, 1 May 2018 21:19:51 +0200
> >> > Peter Zijlstra <peterz@infradead.org> wrote:
> >>
> >> > > Now, lockdep only minimally tracks these otherwise redundant operations;
> >> > > see redundant_hardirqs_{on,off} counters, and loosing that doesn't seen
> >> > > like a big issue.
> >> > >
> >> > > But I'm confused how this helps track superfluous things, it looks like
> >> > > it explicitly tracks _less_ superfluous transitions.
> >> >
> >> > I think it is about triggering on OFF->OFF a warning, as that would
> >> > only happen if we have:
> >> >
> >> > local_irq_save(flags);
> >> > [..]
> >> > local_irq_disable();
> >> >
> >>
> >> Ahh, ok. Yes, that is easier to do with these changes. The alternative
> >> is to add more information to the tracehooks such that we can do the
> >> same internally, but whatever.
> >>
> >> Yeah, I'm fine with the proposed change, but maybe improve the Changelog
> >> a little for slow people like me :-)
> >
> > Great!
> >
> > Nicholas,
> >
> > I know this is an old patch (from last November), but want to send it
> > again with a proper change log and signed off by?
>
> I actually wrote the exact same patch yesterday with changes Matsami
> suggested. However I decided not to send it, since it didn't have any
> performance improvement (which was the reason I wrote it).
>
> Also with my recent set, I don't think it will help detect repeated
> calls to trace_hardirqs_off because we are handling that recursive
> case by using per-cpu variable and bailing out if there is a
> recursion, before even calling into lockdep.
>
> I have mixed feelings about this patch, I am Ok with this patch but I
> suggest its sent with the follow-up patch that shows its use of this.
> And also appreciate if such a follow-up patch is rebased onto the IRQ
> tracepoint work: https://patchwork.kernel.org/patch/10373129/
>
> What do you think?
I'll try to dig it up and resend. Thanks for the feedback on it.
Thanks,
Nick
next prev parent reply other threads:[~2018-05-02 0:12 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-16 16:15 [PATCH] tracing/irqtrace: only call trace_hardirqs_on/off when state changes Nicholas Piggin
2018-05-01 18:46 ` Steven Rostedt
2018-05-01 19:19 ` Peter Zijlstra
2018-05-01 19:38 ` Steven Rostedt
2018-05-01 19:48 ` Peter Zijlstra
2018-05-01 20:00 ` Steven Rostedt
2018-05-01 21:15 ` Joel Fernandes
2018-05-02 0:12 ` Nicholas Piggin [this message]
2018-07-11 1:44 ` Steven Rostedt
2018-07-11 5:58 ` Joel Fernandes
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