Message-ID: <43AAD081.8F510F6B@tv-sign.ru>
Date: Thu, 22 Dec 2005 19:12:49 +0300
From: Oleg Nesterov <oleg@tv-sign.ru>
MIME-Version: 1.0
To: Ingo Molnar <mingo@elte.hu>
Cc: lkml <linux-kernel@vger.kernel.org>, Linus Torvalds <torvalds@osdl.org>,
       Andrew Morton <akpm@osdl.org>, Arjan van de Ven <arjanv@infradead.org>,
       Nicolas Pitre <nico@cam.org>, Jes Sorensen <jes@trained-monkey.org>,
       Zwane Mwaikambo <zwane@arm.linux.org.uk>,
       David Howells <dhowells@redhat.com>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, Benjamin LaHaise <bcrl@kvack.org>,
       Steven Rostedt <rostedt@goodmis.org>,
       Christoph Hellwig <hch@infradead.org>, Andi Kleen <ak@suse.de>,
       Russell King <rmk+lkml@arm.linux.org.uk>
Subject: Re: [patch 5/9] mutex subsystem, core
References: <20051222114233.GF18878@elte.hu> <43AAAC6F.17CC646@tv-sign.ru> <20051222144626.GA31939@elte.hu>
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Ingo Molnar wrote:
> 
> > This is a minor issue, but still I think it makes sense to optimize
> > for uncontended case:
> >
> >       old_val = atomic_xchg(&lock->count, 0); // no sleepers
> >
> >       if (old_val == 1) {
> >               // sleepers ?
> >               if (!list_empty(&lock->wait_list))
> >                       // need to wakeup them
> >                       atomic_set(&lock->count, -1);
> >               ...
> >       }
> >       [*]
> 
> but then we'd have to set it to -1 again, at [*], because we are now

Oh! You are right, thanks.

Oleg.
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