Re: [PATCHv7 18/33] lib/vdso: Add unlikely() hint into vdso_read_begin()
From: Vincenzo Frascino <vincenzo.frascino@arm.com>
Date: 2019-10-16 11:22:21
Also in:
lkml
On 10/11/19 2:23 AM, Dmitry Safonov wrote:
From: Andrei Vagin <redacted>
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 <redacted>
Co-developed-by: Dmitry Safonov <redacted>
Signed-off-by: Dmitry Safonov <redacted>Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
quoted hunk ↗ jump to hunk
--- 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();
-- Regards, Vincenzo