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authorYing Huang <ying.huang@intel.com>2017-08-08 07:30:00 +0300
committerIngo Molnar <mingo@kernel.org>2017-08-29 16:14:38 +0300
commit966a967116e699762dbf4af7f9e0d1955c25aa37 (patch)
tree42d79e5b9df8d67be50b8b87cf5fcdaae751b54b /drivers/cpuidle
parentf52be5708076b75a045ac52c6fef3fffb8300525 (diff)
downloadlinux-966a967116e699762dbf4af7f9e0d1955c25aa37.tar.xz
smp: Avoid using two cache lines for struct call_single_data
struct call_single_data is used in IPIs to transfer information between CPUs. Its size is bigger than sizeof(unsigned long) and less than cache line size. Currently it is not allocated with any explicit alignment requirements. This makes it possible for allocated call_single_data to cross two cache lines, which results in double the number of the cache lines that need to be transferred among CPUs. This can be fixed by requiring call_single_data to be aligned with the size of call_single_data. Currently the size of call_single_data is the power of 2. If we add new fields to call_single_data, we may need to add padding to make sure the size of new definition is the power of 2 as well. Fortunately, this is enforced by GCC, which will report bad sizes. To set alignment requirements of call_single_data to the size of call_single_data, a struct definition and a typedef is used. To test the effect of the patch, I used the vm-scalability multiple thread swap test case (swap-w-seq-mt). The test will create multiple threads and each thread will eat memory until all RAM and part of swap is used, so that huge number of IPIs are triggered when unmapping memory. In the test, the throughput of memory writing improves ~5% compared with misaligned call_single_data, because of faster IPIs. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Huang, Ying <ying.huang@intel.com> [ Add call_single_data_t and align with size of call_single_data. ] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Aaron Lu <aaron.lu@intel.com> Cc: Borislav Petkov <bp@suse.de> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Juergen Gross <jgross@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/87bmnqd6lz.fsf@yhuang-mobile.sh.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'drivers/cpuidle')
-rw-r--r--drivers/cpuidle/coupled.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c
index 71e586d7df71..147f38ea0fcd 100644
--- a/drivers/cpuidle/coupled.c
+++ b/drivers/cpuidle/coupled.c
@@ -119,13 +119,13 @@ struct cpuidle_coupled {
#define CPUIDLE_COUPLED_NOT_IDLE (-1)
-static DEFINE_PER_CPU(struct call_single_data, cpuidle_coupled_poke_cb);
+static DEFINE_PER_CPU(call_single_data_t, cpuidle_coupled_poke_cb);
/*
* The cpuidle_coupled_poke_pending mask is used to avoid calling
- * __smp_call_function_single with the per cpu call_single_data struct already
+ * __smp_call_function_single with the per cpu call_single_data_t struct already
* in use. This prevents a deadlock where two cpus are waiting for each others
- * call_single_data struct to be available
+ * call_single_data_t struct to be available
*/
static cpumask_t cpuidle_coupled_poke_pending;
@@ -339,7 +339,7 @@ static void cpuidle_coupled_handle_poke(void *info)
*/
static void cpuidle_coupled_poke(int cpu)
{
- struct call_single_data *csd = &per_cpu(cpuidle_coupled_poke_cb, cpu);
+ call_single_data_t *csd = &per_cpu(cpuidle_coupled_poke_cb, cpu);
if (!cpumask_test_and_set_cpu(cpu, &cpuidle_coupled_poke_pending))
smp_call_function_single_async(cpu, csd);
@@ -651,7 +651,7 @@ int cpuidle_coupled_register_device(struct cpuidle_device *dev)
{
int cpu;
struct cpuidle_device *other_dev;
- struct call_single_data *csd;
+ call_single_data_t *csd;
struct cpuidle_coupled *coupled;
if (cpumask_empty(&dev->coupled_cpus))