linux-kernel - Re: [PATCH 00/10] jump label: introduce very

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Message-ID: <20120222154733.GA28314@elte.hu>
Date:	Wed, 22 Feb 2012 16:47:33 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	"H. Peter Anvin" <hpa@...or.com>, Jason Baron <jbaron@...hat.com>,
	mathieu.desnoyers@...icios.com, davem@...emloft.net,
	ddaney.cavm@...il.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 00/10] jump label: introduce very_[un]likely + cleanups +
 docs

* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> On Wed, 2012-02-22 at 15:56 +0100, Ingo Molnar wrote:
> > > Again, maybe we need a "very_unlikely()" for the tracing case,
> > 
> > ... and that's the usecase for the scheduler, for events and for 
> > networking. I.e. all current usecases in the kernel 
> 
> The scheduler also really wants the very_likely() variant. We 
> have less use for the unbiased one though.

Yeah, it wants a fastpath and a slowpath and whether it's likely 
or unlikely is situational. So thus it uses both variants in my 
tree:

kernel/sched/core.c:    if (very_unlikely((&paravirt_steal_rq_enabled))) {
kernel/sched/core.c:    if (very_unlikely(&paravirt_steal_enabled)) {
kernel/sched/fair.c:    return very_unlikely(&__cfs_bandwidth_used);
kernel/sched/sched.h:   return very_likely(key); /* Not out of line branch. */
kernel/sched/sched.h:   return very_unlikely(key); /* Out of line branch. */

With no need for an 'unbiased' method.

Let me push out what I have in tip:perf/jump-labels (just 
finished testing it) so that we are all looking at the same 
code.

Thanks,

	Ingo
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