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| author | Andrei Vagin <avagin@gmail.com> | 2019-11-12 01:26:50 +0000 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2020-01-14 12:20:47 +0100 |
| commit | 0898a16a362d436464b34fa644d0d46efc81df92 (patch) | |
| tree | f3cd76906a1a91e0037b5526961a91eaa2697e8b /include/vdso | |
| parent | cdb7c5a9c897ab2e5c56df647dd84c84e150e925 (diff) | |
| download | lwn-0898a16a362d436464b34fa644d0d46efc81df92.tar.gz lwn-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
Diffstat (limited to 'include/vdso')
| -rw-r--r-- | include/vdso/helpers.h | 2 |
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(); |