We have lots of infrastructure in place to partition a multi-core system 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. The patch creates an on_each_cpu_mask infrastructure API (derived from existing arch specific versions in Tile and Arm) and uses it to turn two global IPI invocation to per CPU group invocations. This second version incorporates changes due to reviewers feedback and additional testing. The major changes from the previous version of the patch are: - Better description for some of the patches with examples of what I am trying to solve. - Better coding style for on_each_cpu based on review comments by Peter Zijlstra and Sasha Levin. - Fixed pcp_count handling to take into account which cpu the accounting is done for. Sadly, AFAIK this negates using this_cpu_add/sub as suggested by Peter Z. - Removed kmalloc from the flush_all() path as per review comment by Pekka Enberg. - Moved cpumask allocations for CONFIG_CPUMASK_OFFSTACK=y to a point previous to first use during boot as testing revealed we no longer boot under CONFIG_CPUMASK_OFFSTACK=y with original code. The patch was compiled for arm and boot tested on x86 in UP, SMP, with and without CONFIG_CPUMASK_OFFSTACK and was further tested by running hackbench on x86 in SMP mode in a 4 CPUs VM for several hours with no obvious regressions. I also artificially exercised SLUB flush_all via the debug interface and observed the difference in IPI count across processors with and without the patch - from an IPI on all processors but one without the patch to a subset (and often no IPI at all) with the patch. Signed-off-by: Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx> Acked-by: Chris Metcalf <cmetcalf@xxxxxxxxxx> CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> CC: Frederic Weisbecker <fweisbec@xxxxxxxxx> CC: Russell King <linux@xxxxxxxxxxxxxxxx> CC: linux-mm@xxxxxxxxx CC: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx> CC: Pekka Enberg <penberg@xxxxxxxxxx> CC: Matt Mackall <mpm@xxxxxxxxxxx> CC: Sasha Levin <levinsasha928@xxxxxxxxx> Gilad Ben-Yossef (6): 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 mm: Only IPI CPUs to drain local pages if they exist slub: Only IPI CPUs that have per cpu obj to flush slub: only preallocate cpus_with_slabs if offstack arch/arm/kernel/smp_tlb.c | 20 +++---------- arch/tile/include/asm/smp.h | 7 ----- arch/tile/kernel/smp.c | 19 ------------- include/linux/slub_def.h | 9 ++++++ include/linux/smp.h | 16 +++++++++++ kernel/smp.c | 20 +++++++++++++ mm/page_alloc.c | 64 +++++++++++++++++++++++++++++++++++++------ mm/slub.c | 61 +++++++++++++++++++++++++++++++++++++++- 8 files changed, 164 insertions(+), 52 deletions(-) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>