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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 17:02:19 +1000
Cc: Nick Piggin <>, LKML <>, Andrew Morton <>, Linus Torvalds <>, Ingo Molnar <>, Thomas Gleixner <>, Andi Kleen <>, Martin Mares <>,,,,, Chris Zankel <>, Marc Gauthier <>, Joe Taylor <>, David Mosberger-Tang <>,,,,,,,,,,,,,
In-reply-to: <>
Original-recipient: rfc822;
References: <1145049535.1336.128.camel@localhost.localdomain> <> <> <> <>
Steven Rostedt writes:

> So now I'm asking for advice on some ideas that can be a work around to
> keep the robustness and speed.

Ideally, what I'd like to do on powerpc is to dedicate one register to
storing a per-cpu base address or offset, and be able to resolve the
offset at link time, so that per-cpu variable accesses just become a
register + offset memory access.  (For modules, "link time" would be
module load time.)

We *might* be able to use some of the infrastructure that was put into
gcc and binutils to support TLS (thread local storage) to achieve
this.  (See for some of the
details of that.)

Also, I've added Rusty Russell to the cc list, since he designed the
per-cpu variable stuff in the first place, and would be able to
explain the trade-offs that led to the PERCPU_ENOUGH_ROOM thing.  (I
think you're discovering them as you go, though. :)


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