Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1359532

Re: RFC on fixing mutex spinning on owner

Show all headers | View raw

On Wed, 16 Mar 2016 16:38:56 -0700
Joel Fernandes <agnel.joel@gmail.com> wrote:

> I am not sure if the problem is with the i915 driver, because the
> mutex spin on owner stuff is mutex related so the mutex design may
> potentially need a tweak (I mentioned a proposal of adding mutex
> spinning time outs).
> Also since this is latency issue related (I mentioned preemptoff
> tracer and preempt disabled), I sent it to linux-rt-users. Thanks for
> the tip about sending it to i915 developers, incase no one here has a
> say in the matter, I can drop them a note later as well.

Actually, the preempt off section here is not really an issue:

	rcu_read_lock();
	while (owner_running(lock, owner)) {
		if (need_resched())
			break;

		cpu_relax_lowlatency();
	}
	rcu_read_unlock();

Although preemption may be disabled, that "need_resched()" check will
break out of the loop if a higher priority task were to want to run on
this CPU.

I probably should add a hook there to let the preemptoff tracer know
that this is not an issue.

Thanks for the report.

-- Steve

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

RFC on fixing mutex spinning on owner Joel Fernandes <agnel.joel@gmail.com> - 2016-03-17 00:30 +0100
  Re: RFC on fixing mutex spinning on owner Greg Kroah-Hartman <greg@kroah.com> - 2016-03-17 00:40 +0100
    Re: RFC on fixing mutex spinning on owner Joel Fernandes <agnel.joel@gmail.com> - 2016-03-17 00:40 +0100
      Re: RFC on fixing mutex spinning on owner Steven Rostedt <rostedt@goodmis.org> - 2016-03-17 03:20 +0100
        Re: RFC on fixing mutex spinning on owner Joel Fernandes <agnel.joel@gmail.com> - 2016-03-17 06:40 +0100
          Re: RFC on fixing mutex spinning on owner Steven Rostedt <rostedt@goodmis.org> - 2016-03-17 13:10 +0100
        Re: RFC on fixing mutex spinning on owner Peter Zijlstra <peterz@infradead.org> - 2016-03-17 08:40 +0100
          Re: RFC on fixing mutex spinning on owner Nicholas Mc Guire <der.herr@hofr.at> - 2016-03-17 10:10 +0100
            Re: RFC on fixing mutex spinning on owner Peter Zijlstra <peterz@infradead.org> - 2016-03-17 11:20 +0100
              Re: RFC on fixing mutex spinning on owner Thomas Gleixner <tglx@linutronix.de> - 2016-03-17 12:20 +0100
                Re: RFC on fixing mutex spinning on owner Steven Rostedt <rostedt@goodmis.org> - 2016-03-17 13:10 +0100
                Re: RFC on fixing mutex spinning on owner Peter Zijlstra <peterz@infradead.org> - 2016-03-17 13:20 +0100
                Re: RFC on fixing mutex spinning on owner Thomas Gleixner <tglx@linutronix.de> - 2016-03-17 14:40 +0100
                Re: RFC on fixing mutex spinning on owner Nicholas Mc Guire <der.herr@hofr.at> - 2016-03-17 17:50 +0100

csiph-web