Messages in this thread Patch in this message | | | From | Barry Song <> | Subject | [PATCH v2] irqchip/gic-v3: use dsb(ishst) to synchronize data to smp before issuing ipi | Date | Sun, 20 Feb 2022 19:19:10 +1300 |
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From: Barry Song <song.bao.hua@hisilicon.com>
dsb(ishst) should be enough here as we only need to guarantee the visibility of data to other CPUs in smp inner domain before we send the ipi.
A micro-benchmark is written to verify the performance impact on kunpeng920 machine with 2 sockets, each socket has 2 dies, and each die has 24 CPUs, so totally the system has 2 * 2 * 24 = 96 CPUs. ~2% performance improvement can be seen by this benchmark.
The code of benchmark module:
#include <linux/module.h> #include <linux/timekeeping.h>
volatile int data0 ____cacheline_aligned; volatile int data1 ____cacheline_aligned; volatile int data2 ____cacheline_aligned; volatile int data3 ____cacheline_aligned; volatile int data4 ____cacheline_aligned; volatile int data5 ____cacheline_aligned; volatile int data6 ____cacheline_aligned;
static void ipi_latency_func(void *val) { }
static int __init ipi_latency_init(void) { ktime_t stime, etime, delta; int cpu, i; int start = smp_processor_id();
stime = ktime_get(); for ( i = 0; i < 1000; i++) for (cpu = 0; cpu < 96; cpu++) { data0 = data1 = data2 = data3 = data4 = data5 = data6 = cpu; smp_call_function_single(cpu, ipi_latency_func, NULL, 1); } etime = ktime_get();
delta = ktime_sub(etime, stime);
printk("%s ipi from cpu%d to cpu0-95 delta of 1000times:%lld\n", __func__, start, delta);
return 0; } module_init(ipi_latency_init);
static void ipi_latency_exit(void) { } module_exit(ipi_latency_exit);
MODULE_DESCRIPTION("IPI benchmark"); MODULE_LICENSE("GPL");
run the below commands 10 times on both Vanilla and the kernel with this patch: # taskset -c 0 insmod test.ko # rmmod test
The result on vanilla: ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126757449 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126784249 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126177703 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:127022281 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126184883 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:127374585 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:125778089 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126974441 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:127357625 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126228184
The result on the kernel with this patch: ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:124467401 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123474209 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123558497 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:122993951 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:122984223 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123323609 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:124507583 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123386963 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123340664 ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123285324
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> --- -v2: add benchmark and benchmark data in commit log
drivers/irqchip/irq-gic-v3.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c index 5e935d97207d..0efe1a9a9f3b 100644 --- a/drivers/irqchip/irq-gic-v3.c +++ b/drivers/irqchip/irq-gic-v3.c @@ -1211,7 +1211,7 @@ static void gic_ipi_send_mask(struct irq_data *d, const struct cpumask *mask) * Ensure that stores to Normal memory are visible to the * other CPUs before issuing the IPI. */ - wmb(); + dsb(ishst); for_each_cpu(cpu, mask) { u64 cluster_id = MPIDR_TO_SGI_CLUSTER_ID(cpu_logical_map(cpu)); -- 2.25.1
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