linux-kernel - [this_cpu_xx 00/11] Introduce this_cpu

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Message-Id: <20090605191819.376530498@gentwo.org>
Date:	Fri, 05 Jun 2009 15:18:19 -0400
From:	cl@...ux-foundation.org
To:	linux-kernel@...r.kernel.org
Cc:	davem@...emloft.net
Subject: [this_cpu_xx 00/11] Introduce this_cpu_xx operations

The patchset introduces various operations to allow efficient access
to per cpu variables for the current processor. Currently there is
no way in the core to calcualte the address of the instance
of a per cpu variable without a table lookup through

	per_cpu_ptr(x, smp_processor_id())

The patchset introduces a way to calculate the address using the offset
that is available in arch specific ways (register or special memory
locations) using

	this_cpu_ptr(x)

In addition operations are provided that can operate on per cpu
pointers. This is necessary to be able to use the addresses
generated by the new per cpu allocator with per cpu RMW instructions.

The arch provided RMW instructions can be used to avoid having to switch
off preemption and interrupts for per cpu counter updates.

One caveat with this patchset is that it currently does not work on S/390.
Tejun Heo has a patchset that fixes the SHIFT_PERCPU_PTR issues on that
platform. That patch is required before S/390 will work.

Patchset will reduce the code size and increase speed of operations for
dynamically allocated per cpu based statistics.

Patch shows how this could be done. There are many other places in
the code where these macros could be beneficial.

---

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