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Reduce cross CPU IPI interference

From:  Gilad Ben-Yossef <>
Subject:  [PATCH v9 0/8] Reduce cross CPU IPI interference
Date:  Thu, 9 Feb 2012 10:36:17 +0200
Message-ID:  <>
Cc:  Gilad Ben-Yossef <>
Archive-link:  Article

We have lots of infrastructure in place to partition 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 at times 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 the 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

The patch creates an on_each_cpu_mask and on_each_cpu_cond infrastructure
API (the former derived from existing arch specific versions in Tile and
Arm) and uses them to turn several global IPI invocation to per CPU
group invocations.

This 9th iteration includes comment clarifications (1st and 4th patches) 
and folds in a fix from Andrew Morton for macro parameter handling in UP 
version of on_each_cpu_cond()

The patch set also available from the ipi_noise_v9 branch at

Merge notes: during merge, kindly squash the first three patches to avoid
bisect failures. The last patch in the series is a review helper only.
Please do not merge it.

Gilad Ben-Yossef (8):
  smp: introduce a generic on_each_cpu_mask function
  arm: move arm over to generic on_each_cpu_mask
  tile: move tile to use generic on_each_cpu_mask
  smp: add func to IPI cpus based on parameter func
  slub: only IPI CPUs that have per cpu obj to flush
  fs: only send IPI to invalidate LRU BH when needed
  mm: only IPI CPUs to drain local pages if they exist
  mm: add vmstat counters for tracking PCP drains

 arch/arm/kernel/smp_tlb.c     |   20 ++-------
 arch/tile/include/asm/smp.h   |    7 ---
 arch/tile/kernel/smp.c        |   19 ---------
 fs/buffer.c                   |   15 ++++++-
 include/linux/smp.h           |   47 +++++++++++++++++++++
 include/linux/vm_event_item.h |    1 +
 kernel/smp.c                  |   91 +++++++++++++++++++++++++++++++++++++++++
 mm/page_alloc.c               |   45 +++++++++++++++++++-
 mm/slub.c                     |   10 ++++-
 mm/vmstat.c                   |    2 +
 10 files changed, 212 insertions(+), 45 deletions(-)

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