linux-kernel - Re: [PATCH 4/16] LTTng 0.6.36 for 2.6.18 : atomic UP operations on SMP

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Date:	Mon, 27 Nov 2006 16:56:43 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tom Zanussi <zanussi@...ibm.com>,
	Karim Yaghmour <karim@...rsys.com>,
	Paul Mundt <lethal@...ux-sh.org>, Jes Sorensen <jes@....com>,
	Richard J Moore <richardj_moore@...ibm.com>,
	"Martin J. Bligh" <mbligh@...igh.org>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	Douglas Niehaus <niehaus@...s.ku.edu>, ltt-dev@...fik.org,
	systemtap@...rces.redhat.com
Subject: Re: [PATCH 4/16] LTTng 0.6.36 for 2.6.18 : atomic UP operations on SMP

On Fri, Nov 24, 2006 at 04:55:18PM -0500, Mathieu Desnoyers wrote:
> This patch adds a UP flavor of SMP operations which is intended to provide
> atomic modification of per-cpu data without suffering from the LOCK of memory
> barrier performance cost. Note that extreme care must be taken when accessing
> this data from different CPUs : smp_wmb() and smp_rmb() must be used
> explicitely. As this last scenario happens very rarely in LTTng, it provides a

We already have local_t in asm/local.h for this purposed.  Unfortunately
several architecture implementations are rather suboptimal, but I'm sure
the architecture maintainers would be interested in patches to optimize
the various implementations.

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