Re: [PATCH 00/05] robust per_cpu allocation for modules
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- To: Steven Rostedt <rostedt@xxxxxxxxxxx>
- Subject: Re: [PATCH 00/05] robust per_cpu allocation for modules
- From: Paul Mackerras <paulus@xxxxxxxxx>
- Date: Sun, 16 Apr 2006 16:35:09 +1000
- Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxx>, linux-mips@xxxxxxxxxxxxxx, David Mosberger-Tang <davidm@xxxxxxxxxx>, linux-ia64@xxxxxxxxxxxxxxx, Martin Mares <mj@xxxxxxxxxxxxxxxxxxxxxxxx>, spyro@xxxxxxx, Joe Taylor <joe@xxxxxxxxxxxxx>, linuxppc-dev@xxxxxxxxxx, benedict.gaster@xxxxxxxxxx, bjornw@xxxxxxxx, Ingo Molnar <mingo@xxxxxxx>, grundler@xxxxxxxxxxxxxxxx, starvik@xxxxxxxx, Linus Torvalds <torvalds@xxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, rth@xxxxxxxxxxx, chris@xxxxxxxxxx, tony.luck@xxxxxxxxx, Andi Kleen <ak@xxxxxxx>, ralf@xxxxxxxxxxxxxx, Marc Gauthier <marc@xxxxxxxxxxxxx>, lethal@xxxxxxxxxxxx, schwidefsky@xxxxxxxxxx, linux390@xxxxxxxxxx, davem@xxxxxxxxxxxxx, parisc-linux@xxxxxxxxxxxxxxxx
- In-reply-to: <1145049535.1336.128.camel@xxxxxxxxxxxxxxxxxxxxx>
- References: <1145049535.1336.128.camel@xxxxxxxxxxxxxxxxxxxxx>
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?
Paul.
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