From 0898a16a362d436464b34fa644d0d46efc81df92 Mon Sep 17 00:00:00 2001 From: Andrei Vagin Date: Tue, 12 Nov 2019 01:26:50 +0000 Subject: lib/vdso: Add unlikely() hint into vdso_read_begin() Place the branch with no concurrent write before the contended case. Performance numbers for Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz (more clock_gettime() cycles - the better): | before | after ----------------------------------- | 150252214 | 153242367 | 150301112 | 153324800 | 150392773 | 153125401 | 150373957 | 153399355 | 150303157 | 153489417 | 150365237 | 153494270 ----------------------------------- avg | 150331408 | 153345935 diff % | 2 | 0 ----------------------------------- stdev % | 0.3 | 0.1 Co-developed-by: Dmitry Safonov Signed-off-by: Andrei Vagin Signed-off-by: Dmitry Safonov Signed-off-by: Thomas Gleixner Tested-by: Vincenzo Frascino Reviewed-by: Vincenzo Frascino Link: https://lore.kernel.org/r/20191112012724.250792-2-dima@arista.com --- include/vdso/helpers.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include') diff --git a/include/vdso/helpers.h b/include/vdso/helpers.h index 01641dbb68ef..9a2af9fca45e 100644 --- a/include/vdso/helpers.h +++ b/include/vdso/helpers.h @@ -10,7 +10,7 @@ static __always_inline u32 vdso_read_begin(const struct vdso_data *vd) { u32 seq; - while ((seq = READ_ONCE(vd->seq)) & 1) + while (unlikely((seq = READ_ONCE(vd->seq)) & 1)) cpu_relax(); smp_rmb(); -- cgit v1.2.3-59-g8ed1b