linux-kernel - Re: [PATCH 2/6] sched,trace: Add a tracepoint for remote wakeups via polling

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Message-ID: <20140604135458.GN30445@twins.programming.kicks-ass.net>
Date:	Wed, 4 Jun 2014 15:54:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	Andy Lutomirski <luto@...capital.net>, umgwanakikbuti@...il.com,
	mingo@...nel.org, tglx@...utronix.de, nicolas.pitre@...aro.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] sched,trace: Add a tracepoint for remote wakeups via
 polling

On Wed, Jun 04, 2014 at 03:00:26PM +0200, Daniel Lezcano wrote:
> On 06/04/2014 02:29 AM, Andy Lutomirski wrote:
> >Remote wakeups of polling CPUs are a valuable performance
> >improvement; add a tracepoint to make it much easier to verify that
> >they're working.
> >
> >Signed-off-by: Andy Lutomirski <luto@...capital.net>
> 
> I don't think this trace makes sense. The polling state is x86 only and this
> trace is in the generic code.

Not so, there's PPC using it someplace (ISTR its doing a polling
amortization of the idle hypercall or somesuch) and there's archs that
have no other idle means that polling, as well as some for which its
optional.

There are indeed archs, like arm, that only do the WFI thing, and for
those this is indeed all a NOP.



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