The following commit has been merged into the timers/core branch of tip: Commit-ID: 79472606d6fba66c20299f4121a657ce73efc302 Gitweb: https://git.kernel.org/tip/79472606d6fba66c20299f4121a657ce73efc302 Author: Andrei Vagin <avagin@xxxxxxxxx> AuthorDate: Tue, 12 Nov 2019 01:26:50 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Mon, 13 Jan 2020 08:10:46 +01:00 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 <dima@xxxxxxxxxx> Signed-off-by: Andrei Vagin <avagin@xxxxxxxxx> Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Tested-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Link: https://lore.kernel.org/r/20191112012724.250792-2-dima@xxxxxxxxxx --- include/vdso/helpers.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/vdso/helpers.h b/include/vdso/helpers.h index 01641db..9a2af9f 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();