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lib/vdso: Add unlikely() hint into vdso_read_begin()
author
Andrei Vagin
<avagin@gmail.com>
Tue, 12 Nov 2019 01:26:50 +0000
(
01:26
+0000)
committer
Thomas Gleixner
<tglx@linutronix.de>
Tue, 14 Jan 2020 11:20:47 +0000
(12:20 +0100)
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
include/vdso/helpers.h
patch
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blob
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diff --git
a/include/vdso/helpers.h
b/include/vdso/helpers.h
index
01641db
..
9a2af9f
100644
(file)
--- 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();