aboutsummaryrefslogtreecommitdiffstats
path: root/kernel/smp.c
diff options
context:
space:
mode:
authorYing Huang <ying.huang@intel.com>2017-08-08 12:30:00 +0800
committerIngo Molnar <mingo@kernel.org>2017-08-29 15:14:38 +0200
commit966a967116e699762dbf4af7f9e0d1955c25aa37 (patch)
tree42d79e5b9df8d67be50b8b87cf5fcdaae751b54b /kernel/smp.c
parentlocking/lockdep: Untangle xhlock history save/restore from task independence (diff)
downloadlinux-dev-966a967116e699762dbf4af7f9e0d1955c25aa37.tar.xz
linux-dev-966a967116e699762dbf4af7f9e0d1955c25aa37.zip
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 '')
-rw-r--r--kernel/smp.c32
1 files changed, 17 insertions, 15 deletions
diff --git a/kernel/smp.c b/kernel/smp.c
index 3061483cb3ad..81cfca9b4cc3 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -28,7 +28,7 @@ enum {
};
struct call_function_data {
- struct call_single_data __percpu *csd;
+ call_single_data_t __percpu *csd;
cpumask_var_t cpumask;
cpumask_var_t cpumask_ipi;
};
@@ -51,7 +51,7 @@ int smpcfd_prepare_cpu(unsigned int cpu)
free_cpumask_var(cfd->cpumask);
return -ENOMEM;
}
- cfd->csd = alloc_percpu(struct call_single_data);
+ cfd->csd = alloc_percpu(call_single_data_t);
if (!cfd->csd) {
free_cpumask_var(cfd->cpumask);
free_cpumask_var(cfd->cpumask_ipi);
@@ -103,12 +103,12 @@ void __init call_function_init(void)
* previous function call. For multi-cpu calls its even more interesting
* as we'll have to ensure no other cpu is observing our csd.
*/
-static __always_inline void csd_lock_wait(struct call_single_data *csd)
+static __always_inline void csd_lock_wait(call_single_data_t *csd)
{
smp_cond_load_acquire(&csd->flags, !(VAL & CSD_FLAG_LOCK));
}
-static __always_inline void csd_lock(struct call_single_data *csd)
+static __always_inline void csd_lock(call_single_data_t *csd)
{
csd_lock_wait(csd);
csd->flags |= CSD_FLAG_LOCK;
@@ -116,12 +116,12 @@ static __always_inline void csd_lock(struct call_single_data *csd)
/*
* prevent CPU from reordering the above assignment
* to ->flags with any subsequent assignments to other
- * fields of the specified call_single_data structure:
+ * fields of the specified call_single_data_t structure:
*/
smp_wmb();
}
-static __always_inline void csd_unlock(struct call_single_data *csd)
+static __always_inline void csd_unlock(call_single_data_t *csd)
{
WARN_ON(!(csd->flags & CSD_FLAG_LOCK));
@@ -131,14 +131,14 @@ static __always_inline void csd_unlock(struct call_single_data *csd)
smp_store_release(&csd->flags, 0);
}
-static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_data, csd_data);
+static DEFINE_PER_CPU_SHARED_ALIGNED(call_single_data_t, csd_data);
/*
- * Insert a previously allocated call_single_data element
+ * Insert a previously allocated call_single_data_t element
* for execution on the given CPU. data must already have
* ->func, ->info, and ->flags set.
*/
-static int generic_exec_single(int cpu, struct call_single_data *csd,
+static int generic_exec_single(int cpu, call_single_data_t *csd,
smp_call_func_t func, void *info)
{
if (cpu == smp_processor_id()) {
@@ -210,7 +210,7 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline)
{
struct llist_head *head;
struct llist_node *entry;
- struct call_single_data *csd, *csd_next;
+ call_single_data_t *csd, *csd_next;
static bool warned;
WARN_ON(!irqs_disabled());
@@ -268,8 +268,10 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline)
int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
int wait)
{
- struct call_single_data *csd;
- struct call_single_data csd_stack = { .flags = CSD_FLAG_LOCK | CSD_FLAG_SYNCHRONOUS };
+ call_single_data_t *csd;
+ call_single_data_t csd_stack = {
+ .flags = CSD_FLAG_LOCK | CSD_FLAG_SYNCHRONOUS,
+ };
int this_cpu;
int err;
@@ -321,7 +323,7 @@ EXPORT_SYMBOL(smp_call_function_single);
* NOTE: Be careful, there is unfortunately no current debugging facility to
* validate the correctness of this serialization.
*/
-int smp_call_function_single_async(int cpu, struct call_single_data *csd)
+int smp_call_function_single_async(int cpu, call_single_data_t *csd)
{
int err = 0;
@@ -444,7 +446,7 @@ void smp_call_function_many(const struct cpumask *mask,
cpumask_clear(cfd->cpumask_ipi);
for_each_cpu(cpu, cfd->cpumask) {
- struct call_single_data *csd = per_cpu_ptr(cfd->csd, cpu);
+ call_single_data_t *csd = per_cpu_ptr(cfd->csd, cpu);
csd_lock(csd);
if (wait)
@@ -460,7 +462,7 @@ void smp_call_function_many(const struct cpumask *mask,
if (wait) {
for_each_cpu(cpu, cfd->cpumask) {
- struct call_single_data *csd;
+ call_single_data_t *csd;
csd = per_cpu_ptr(cfd->csd, cpu);
csd_lock_wait(csd);