linux-kernel - [PATCH 0/4] percpu: Optimize percpu accesses

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Message-Id: <20080604003018.538497000@polaris-admin.engr.sgi.com>
Date:	Tue, 03 Jun 2008 17:30:18 -0700
From:	Mike Travis <travis@....com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 0/4] percpu: Optimize percpu accesses


This patchset provides the following:

  * Generic: Percpu infrastructure to rebase the per cpu area to zero

    This provides for the capability of accessing the percpu variables
    using a local register instead of having to go through a table
    on node 0 to find the cpu-specific offsets.  It also would allow
    atomic operations on percpu variables to reduce required locking.
    Uses a new config var HAVE_ZERO_BASED_PER_CPU to indicate to the
    generic code that the arch has this new basing.

  * x86_64: Fold pda into per cpu area

    Declare the pda as a per cpu variable. This will move the pda
    area to an address accessible by the x86_64 per cpu macros.
    Subtraction of __per_cpu_start will make the offset based from
    the beginning of the per cpu area.  Since %gs is pointing to the
    pda, it will then also point to the per cpu variables and can be
    accessed thusly:

	%gs:[&per_cpu_xxxx - __per_cpu_start]

  * x86_64: Rebase per cpu variables to zero

    Take advantage of the zero-based per cpu area provided above.
    Then we can directly use the x86_32 percpu operations. x86_32
    offsets %fs by __per_cpu_start. x86_64 has %gs pointing directly
    to the pda and the per cpu area thereby allowing access to the
    pda with the x86_64 pda operations and access to the per cpu
    variables using x86_32 percpu operations.


Based on linux-2.6.tip

Signed-off-by: Christoph Lameter <clameter@....com>
Signed-off-by: Mike Travis <travis@....com>
---

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