| From | Dmitry Safonov <> | Subject | [PATCHv8 01/34] lib/vdso: Add unlikely() hint into vdso_read_begin() | Date | Tue, 12 Nov 2019 01:26:50 +0000 |
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From: Andrei Vagin <avagin@gmail.com>
Place the branch with no concurrent write before 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
Signed-off-by: Andrei Vagin <avagin@gmail.com> Co-developed-by: Dmitry Safonov <dima@arista.com> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Signed-off-by: Dmitry Safonov <dima@arista.com> --- 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 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(); -- 2.24.0
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