• Gilad Ben-Yossef's avatar
    smp: introduce a generic on_each_cpu_mask() function · 3fc498f1
    Gilad Ben-Yossef authored
    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
    paths.
    
    This 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.
    
    Core kernel:
    
    on_each_cpu_mask() calls a function on processors specified by cpumask,
    which may or may not include the local processor.
    
    You must not call this function with disabled interrupts or from a
    hardware interrupt handler or from a bottom half handler.
    
    arch/arm:
    
    Note that the generic version is a little different then the Arm one:
    
    1. It has the mask as first parameter
    2. It calls the function on the calling CPU with interrupts disabled,
       but this should be OK since the function is called on the other CPUs
       with interrupts disabled anyway.
    
    arch/tile:
    
    The API is the same as the tile private one, but the generic version
    also calls the function on the with interrupts disabled in UP case
    
    This is OK since the function is called on the other CPUs
    with interrupts disabled.
    Signed-off-by: default avatarGilad Ben-Yossef <gilad@benyossef.com>
    Reviewed-by: default avatarChristoph Lameter <cl@linux.com>
    Acked-by: default avatarChris Metcalf <cmetcalf@tilera.com>
    Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Russell King <linux@arm.linux.org.uk>
    Cc: Pekka Enberg <penberg@kernel.org>
    Cc: Matt Mackall <mpm@selenic.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Andi Kleen <andi@firstfloor.org>
    Cc: Sasha Levin <levinsasha928@gmail.com>
    Cc: Mel Gorman <mel@csn.ul.ie>
    Cc: Alexander Viro <viro@zeniv.linux.org.uk>
    Cc: Avi Kivity <avi@redhat.com>
    Acked-by: default avatarMichal Nazarewicz <mina86@mina86.org>
    Cc: Kosaki Motohiro <kosaki.motohiro@gmail.com>
    Cc: Milton Miller <miltonm@bga.com>
    Cc: Russell King <linux@arm.linux.org.uk>
    Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    3fc498f1
smp.h 3.99 KB