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Re: [PATCH 00/05] robust per_cpu allocation for modules

To: Steven Rostedt <>
Subject: Re: [PATCH 00/05] robust per_cpu allocation for modules
From: Paul Mackerras <>
Date: Sun, 16 Apr 2006 16:35:09 +1000
Cc: LKML <>, Andrew Morton <>,, David Mosberger-Tang <>,, Martin Mares <>,, Joe Taylor <>,,,, Ingo Molnar <>,,, Linus Torvalds <>, Thomas Gleixner <>,,,, Andi Kleen <>,, Marc Gauthier <>,,,,,
In-reply-to: <1145049535.1336.128.camel@localhost.localdomain>
Original-recipient: rfc822;
References: <1145049535.1336.128.camel@localhost.localdomain>
Steven Rostedt writes:

> The data in .data.percpu_offset holds is referenced by the per_cpu
> variable name which points to the __per_cpu_offset array.  For modules,
> it will point to the per_cpu_offset array of the module.
> Example:
>  DEFINE_PER_CPU(int, myint);
>  would now create a variable called per_cpu_offset__myint in
> the .data.percpu_offset section.  This variable will point to the (if
> defined in the kernel) __per_cpu_offset[] array.  If this was a module
> variable, it would point to the module per_cpu_offset[] array which is
> created when the modules is loaded.

This sounds like you have an extra memory reference each time a
per-cpu variable is accessed.  Have you tried to measure the
performance impact of that?  If so, how much performance does it lose?


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