linux-kernel - Re: [PATCH v2] tracing: Don't account for cpu idle time with irqsoff tracers

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Message-ID: <20140528072457.GM11096@twins.programming.kicks-ass.net>
Date:	Wed, 28 May 2014 09:24:57 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Stephen Boyd <sboyd@...eaurora.org>, Arnd Bergmann <arnd@...db.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Corey Minyard <cminyard@...sta.com>,
	Stanislav Meduna <stano@...una.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	john.stultz@...aro.org
Subject: Re: [PATCH v2] tracing: Don't account for cpu idle time with irqsoff
 tracers

On Tue, May 27, 2014 at 08:42:14PM -0400, Steven Rostedt wrote:
> On Tue, 2014-05-27 at 17:11 -0700, Stephen Boyd wrote:
> 
> > cpuidle_enter_state() calls ktime_get() which on lockdep enabled builds
> > calls seqcount_lockdep_reader_access() which calls local_irq_save() that
> 
> seqcount_lockdep_reader_access()?? Ug, I wonder if that should call
> raw_local_irq_save/restore() as it's a lockdep helper to begin with. If
> it's wrong then it's the lockdep infrastructure that broke, not the core
> kernel.
> 
> Peter?

Hurm,.. don't know actually.. so from a lockdep pov it doesn't need to
do that and we can simply remove the local_irq_{save,restore}() from
that function.

It could be John did it to avoid some IRQ recursion warning, but if so,
he failed to mention it.

John, remember why you typed those characters?

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