lib/vdso: Add unlikely() hint into vdso_read_begin()
authorAndrei Vagin <avagin@gmail.com>
Tue, 12 Nov 2019 01:26:50 +0000 (01:26 +0000)
committerThomas Gleixner <tglx@linutronix.de>
Tue, 14 Jan 2020 11:20:47 +0000 (12:20 +0100)
commit0898a16a362d436464b34fa644d0d46efc81df92
treef3cd76906a1a91e0037b5526961a91eaa2697e8b
parentcdb7c5a9c897ab2e5c56df647dd84c84e150e925
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
include/vdso/helpers.h