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SubjectRe: [PATCHv7 18/33] lib/vdso: Add unlikely() hint into vdso_read_begin()
On Wed, Oct 16, 2019 at 12:24:14PM +0100, Vincenzo Frascino wrote:
> On 10/11/19 2:23 AM, Dmitry Safonov wrote:
> > 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>
> > Signed-off-by: Dmitry Safonov <dima@arista.com>
>
> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

Hello Vincenzo,

Could you test the attached patch on aarch64? On x86, it gives about 9%
performance improvement for CLOCK_MONOTONIC and CLOCK_BOOTTIME.

Here is my test:
https://github.com/avagin/vdso-perf

It is calling clock_gettime() in a loop for three seconds and then
reports a number of iterations.

Thanks,
Andrei
From 5252093fec4c74802e5ef501b9f1db3369430c80 Mon Sep 17 00:00:00 2001
From: Andrei Vagin <avagin@gmail.com>
Date: Tue, 22 Oct 2019 18:23:17 -0700
Subject: [PATCH] lib/vdso: make do_hres and do_coarse as __always_inline

Performance numbers for Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz
(more clock_gettime() cycles - the better):

clock | before | after | diff
----------------------------------------------------------
monotonic | 153222105 | 166775025 | 8.8%
monotonic-coarse | 671557054 | 691513017 | 3.0%
monotonic-raw | 147116067 | 161057395 | 9.5%
boottime | 153446224 | 166962668 | 9.1%

Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
lib/vdso/gettimeofday.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index e630e7ff57f1..b4f7f0f246af 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -38,7 +38,7 @@ u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult)
}
#endif

-static int do_hres(const struct vdso_data *vd, clockid_t clk,
+static __always_inline int do_hres(const struct vdso_data *vd, clockid_t clk,
struct __kernel_timespec *ts)
{
const struct vdso_timestamp *vdso_ts = &vd->basetime[clk];
@@ -68,7 +68,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk,
return 0;
}

-static void do_coarse(const struct vdso_data *vd, clockid_t clk,
+static __always_inline void do_coarse(const struct vdso_data *vd, clockid_t clk,
struct __kernel_timespec *ts)
{
const struct vdso_timestamp *vdso_ts = &vd->basetime[clk];
@@ -97,12 +97,16 @@ __cvdso_clock_gettime_common(clockid_t clock, struct __kernel_timespec *ts)
*/
msk = 1U << clock;
if (likely(msk & VDSO_HRES)) {
- return do_hres(&vd[CS_HRES_COARSE], clock, ts);
+ vd = &vd[CS_HRES_COARSE];
+out_hres:
+ return do_hres(vd, clock, ts);
} else if (msk & VDSO_COARSE) {
do_coarse(&vd[CS_HRES_COARSE], clock, ts);
return 0;
} else if (msk & VDSO_RAW) {
- return do_hres(&vd[CS_RAW], clock, ts);
+ vd = &vd[CS_RAW];
+ /* goto allows to avoid extra inlining of do_hres. */
+ goto out_hres;
}
return -1;
}
--
2.21.0
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