From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrea Righi <righi.andrea@gmail.com>,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] mm: unify pmd_free() implementation
Date: Mon, 28 Jul 2008 11:17:32 -0500 [thread overview]
Message-ID: <1217261852.3503.89.camel@localhost.localdomain> (raw)
In-Reply-To: <alpine.LFD.1.10.0807280851130.3486@nehalem.linux-foundation.org>
On Mon, 2008-07-28 at 08:53 -0700, Linus Torvalds wrote:
> But this is horrible, because it forces a totally unnecessary function
> call for that empty function.
>
> Yeah, the function will be cheap, but the call itself will not be (it's a
> C language barrier and basically disables optimizations around it, causing
> thigns like register spill/reload for no good reason).
Are you sure about this (the barrier)? We've been struggling to find a
paradigm for our trace points but the consensus seemed to be that
compiler barriers were pretty tiny perturbations in the optimiser stream
(they affect calculation ordering, but not usually enough to be
noticed). The register spills to get known locations for the tracepoint
variables seemed to be the much more expensive thing.
If this basic assumption is wrong, we need to know now ...
James
next prev parent reply other threads:[~2008-07-28 16:18 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-07-28 15:51 [PATCH 1/1] mm: unify pmd_free() implementation Andrea Righi
2008-07-28 15:53 ` Linus Torvalds
2008-07-28 16:17 ` Andrea Righi
2008-07-28 16:17 ` Andrea Righi
2008-07-28 16:27 ` KOSAKI Motohiro
2008-07-28 17:19 ` Andrea Righi
2008-07-28 20:30 ` Andrew Morton
2008-07-28 20:46 ` Jeremy Fitzhardinge
2008-07-28 22:53 ` [PATCH 1/1] mm: unify pmd_free() and __pmd_free_tlb() implementation Andrea Righi
2008-07-31 16:17 ` Ingo Molnar
2008-07-31 16:59 ` Andrea Righi
2008-07-28 16:17 ` James Bottomley [this message]
2008-07-28 16:45 ` [PATCH 1/1] mm: unify pmd_free() implementation Linus Torvalds
2008-07-28 16:58 ` James Bottomley
2008-07-28 17:10 ` Linus Torvalds
2008-07-28 20:08 ` [PATCH 1/1] mm: unify pmd_free() implementation -> instrumentation Mathieu Desnoyers
2008-07-28 20:08 ` Mathieu Desnoyers
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