linux-kernel - Re: [PATCH 3/3] perf: Fix mux

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Message-ID: <20150415142002.GR23123@twins.programming.kicks-ass.net>
Date:	Wed, 15 Apr 2015 16:20:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Ahern <dsahern@...il.com>
Cc:	tglx@...utronix.de, mingo@...nel.org, linux-kernel@...r.kernel.org,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 3/3] perf: Fix mux_interval hrtimer wreckage

On Wed, Apr 15, 2015 at 07:48:02AM -0600, David Ahern wrote:
> Hi Peter:
> 
> On 4/15/15 3:41 AM, Peter Zijlstra wrote:
> >Thomas stumbled over the hrtimer_forward_now() in
> >perf_event_mux_interval_ms_store() and noticed its broken-ness.
> >
> >You cannot just change the expiry time of an active timer, it will
> >destroy the red-black tree order and cause havoc.
> >
> >Change it to (re)start the timer instead, (re)starting a timer will
> >dequeue and enqueue a timer and therefore preserve rb-tree order.
> 
> Should this be fixed in stable trees as well?

Hmm, I was going to write how this all relies on the hrtimer rework, but
I think we might just be fine because all this is strictly cpu local and
serialized through irq-disable.

But yes, its can't be worse than it is now.
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