From 3fc498f165304dc913f1d13b5ac9ab4c758ee7ab Mon Sep 17 00:00:00 2001 From: Gilad Ben-Yossef Date: Wed, 28 Mar 2012 14:42:43 -0700 Subject: smp: introduce a generic on_each_cpu_mask() function 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: Gilad Ben-Yossef Reviewed-by: Christoph Lameter Acked-by: Chris Metcalf Acked-by: Peter Zijlstra Cc: Frederic Weisbecker Cc: Russell King Cc: Pekka Enberg Cc: Matt Mackall Cc: Rik van Riel Cc: Andi Kleen Cc: Sasha Levin Cc: Mel Gorman Cc: Alexander Viro Cc: Avi Kivity Acked-by: Michal Nazarewicz Cc: Kosaki Motohiro Cc: Milton Miller Cc: Russell King Acked-by: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/smp.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) (limited to 'include') diff --git a/include/linux/smp.h b/include/linux/smp.h index 8cc38d3bab0c..d0adb7898d54 100644 --- a/include/linux/smp.h +++ b/include/linux/smp.h @@ -101,6 +101,13 @@ static inline void call_function_init(void) { } */ int on_each_cpu(smp_call_func_t func, void *info, int wait); +/* + * Call a function on processors specified by mask, which might include + * the local one. + */ +void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func, + void *info, bool wait); + /* * Mark the boot cpu "online" so that it can call console drivers in * printk() and can access its per-cpu storage. @@ -132,6 +139,21 @@ static inline int up_smp_call_function(smp_call_func_t func, void *info) local_irq_enable(); \ 0; \ }) +/* + * Note we still need to test the mask even for UP + * because we actually can get an empty mask from + * code that on SMP might call us without the local + * CPU in the mask. + */ +#define on_each_cpu_mask(mask, func, info, wait) \ + do { \ + if (cpumask_test_cpu(0, (mask))) { \ + local_irq_disable(); \ + (func)(info); \ + local_irq_enable(); \ + } \ + } while (0) + static inline void smp_send_reschedule(int cpu) { } #define num_booting_cpus() 1 #define smp_prepare_boot_cpu() do {} while (0) -- cgit v1.2.3