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authorAndrei Vagin <avagin@gmail.com>2019-11-12 01:26:50 +0000
committerThomas Gleixner <tglx@linutronix.de>2020-01-14 12:20:47 +0100
commit0898a16a362d436464b34fa644d0d46efc81df92 (patch)
treef3cd76906a1a91e0037b5526961a91eaa2697e8b
parentlib/vdso: Avoid duplication in __cvdso_clock_getres() (diff)
downloadlinux-dev-0898a16a362d436464b34fa644d0d46efc81df92.tar.xz
linux-dev-0898a16a362d436464b34fa644d0d46efc81df92.zip
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@arista.com> Signed-off-by: Andrei Vagin <avagin@gmail.com> Signed-off-by: Dmitry Safonov <dima@arista.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Link: https://lore.kernel.org/r/20191112012724.250792-2-dima@arista.com
-rw-r--r--include/vdso/helpers.h2
1 files changed, 1 insertions, 1 deletions
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();