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SubjectRe: [PATCH v6 0/8] Reduce cross CPU IPI interference
On 1/8/2012 11:26 AM, Gilad Ben-Yossef wrote:
> We have lots of infrastructure in place to partition a multi-core systems
> such that we have a group of CPUs that are dedicated to specific task:
> cgroups, scheduler and interrupt affinity and cpuisol boot parameter.
> Still, kernel code will some time interrupt all CPUs in the system via IPIs
> for various needs. These IPIs are useful and cannot be avoided altogether,
> but in certain cases it is possible to interrupt only specific CPUs that
> have useful work to do and not the entire system.
> This patch set, inspired by discussions with Peter Zijlstra and Frederic
> Weisbecker when testing the nohz task patch set, is a first stab at trying
> to explore doing this by locating the places where such global IPI calls
> are being made and turning a global IPI into an IPI for a specific group
> of CPUs. The purpose of the patch set is to get feedback if this is the
> right way to go for dealing with this issue and indeed, if the issue is
> even worth dealing with at all. Based on the feedback from this patch set
> I plan to offer further patches that address similar issue in other code
> paths.
> The patch creates an on_each_cpu_mask and on_each_cpu_conf infrastructure
> API (the former derived from existing arch specific versions in Tile and
> Arm) and and uses them to turn several global IPI invocation to per CPU
> group invocations.

Acked-by: Chris Metcalf <>

(To be fair, mostly this acks the proposed infrastructure, and moving the
functions out of the tile architecture and into the generic code; I not
expert enough at slub or the invalidate_bh_lrus path to ack those changes,
other than to say I like how they look.)

Chris Metcalf, Tilera Corp.

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