path: root/block/blk-softirq.c
diff options
authorYing Huang <>2017-08-08 12:30:00 +0800
committerIngo Molnar <>2017-08-29 15:14:38 +0200
commit966a967116e699762dbf4af7f9e0d1955c25aa37 (patch)
tree42d79e5b9df8d67be50b8b87cf5fcdaae751b54b /block/blk-softirq.c
parentf52be5708076b75a045ac52c6fef3fffb8300525 (diff)
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 <> Signed-off-by: Huang, Ying <> [ Add call_single_data_t and align with size of call_single_data. ] Signed-off-by: Peter Zijlstra (Intel) <> Cc: Aaron Lu <> Cc: Borislav Petkov <> Cc: Eric Dumazet <> Cc: Juergen Gross <> Cc: Linus Torvalds <> Cc: Michael Ellerman <> Cc: Thomas Gleixner <> Link: Signed-off-by: Ingo Molnar <>
Diffstat (limited to 'block/blk-softirq.c')
1 files changed, 1 insertions, 1 deletions
diff --git a/block/blk-softirq.c b/block/blk-softirq.c
index 87b7df4..07125e7 100644
--- a/block/blk-softirq.c
+++ b/block/blk-softirq.c
@@ -60,7 +60,7 @@ static void trigger_softirq(void *data)
static int raise_blk_irq(int cpu, struct request *rq)
if (cpu_online(cpu)) {
- struct call_single_data *data = &rq->csd;
+ call_single_data_t *data = &rq->csd;
data->func = trigger_softirq;
data->info = rq;