linux-kernel - Re: [PATCH, take4] FUTEX : new PRIVATE futexes

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Date:	Thu, 12 Apr 2007 11:57:02 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>,
	Ulrich Drepper <drepper@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...e.de>,
	Ravikiran G Thirumalai <kiran@...lex86.org>,
	"Shai Fultheim (Shai@...lex86.org)" <shai@...lex86.org>,
	pravin b shelar <pravin.shelar@...softinc.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH, take4] FUTEX : new PRIVATE futexes

Eric Dumazet wrote:
> On Wed, 11 Apr 2007 19:23:26 +1000
> Nick Piggin <nickpiggin@...oo.com.au> wrote:

>>>As this external thing certainly is not doing the check itself, to be on the safe side we should enforce it in get_futex_key(). I agree with you : If we want to maximize performance, we could say : The check *must* be done by the caller.
>>
>>Well we _control_ the API, so let's make it as clean and performant as possible
>>from the start.
> 
> 
> Take a look at do_futex().
> Adding checks in callers just increase code size. I tried this got only bad results.
> This would speedup only the slow path (ie when some user code want to give us non aligned addrs)
> A single factorized check is cleaner and not slower, since we reduce icache pressure.

1 extra check versus all that additional argument passing? I don't think it
is conclusive.

-- 
SUSE Labs, Novell Inc.
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