linux-kernel - RE: [patch] speed up single bio

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Message-ID: <000001c71a80$90342120$f180030a@amr.corp.intel.com>
Date:	Thu, 7 Dec 2006 20:23:07 -0800
From:	"Chen, Kenneth W" <kenneth.w.chen@...el.com>
To:	<ak@...e.de>
Cc:	"linux-kernel" <linux-kernel@...r.kernel.org>
Subject: RE: [patch] speed up single bio_vec allocation

Andi Kleen wrote on Thursday, December 07, 2006 6:28 PM
> "Chen, Kenneth W" <kenneth.w.chen@...el.com> writes:
> > I tried to use cache_line_size() to find out the alignment of struct bio, but
> > stumbled on that it is a runtime function for x86_64.
> 
> It's a single global variable access:
> 
> #define cache_line_size() (boot_cpu_data.x86_cache_alignment)
> 
> Or do you mean it caused cache misses?  boot_cpu_data is cache aligned
> and practically read only, so there shouldn't be any false sharing at least.

No, I was looking for a generic constant that describes cache line size.
I needed a constant in order to avoid runtime check and to rely on compiler
to optimize a conditional check away.
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