linux-kernel - Re: spinlocks -- why are releases inlined and acquires are not?

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Message-ID: <20080401084308.GA4787@elte.hu>
Date:	Tue, 1 Apr 2008 10:43:08 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: spinlocks -- why are releases inlined and acquires are not?


* Jiri Kosina <jkosina@...e.cz> wrote:

> In fact we have received report from one of our users that he is 
> seeing approximately 15% performance degradation of mmap() when 
> spinlocks are not inlined. I am going to do some performance 
> measurements myself shortly, as it seems quite strange, but while at 
> it, I have noticed the aforementioned asymetry in spinlock.h, so I 
> just wanted to know if there is any particular reason behind that.

inlining decisions almost never have effects of that order of magnitude 
- especially on new CPUs, so that 15% looks quite suspicious to me. If 
it's real then an easy-to-run testcase would be nice.

	Ingo
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