From: Alexander Sverdlin <[email protected]>
This is a preparation for CLOCK_MONOTONIC_RAW vDSO implementation.
Coincidentally it had a slight performance improvement as well:
---- Test code ----
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#define CLOCK_TYPE CLOCK_MONOTONIC_RAW
#define DURATION_SEC 10
int main(int argc, char **argv)
{
struct timespec t, end;
unsigned long long cnt = 0;
clock_gettime(CLOCK_TYPE, &end);
end.tv_sec += DURATION_SEC;
do {
clock_gettime(CLOCK_TYPE, &t);
++cnt;
} while (t.tv_sec < end.tv_sec || t.tv_nsec < end.tv_nsec);
dprintf(STDOUT_FILENO, "%llu", cnt);
return EXIT_SUCCESS;
}
-------------------
The results from the above test program:
Clock Before After Diff
----- ------ ----- ----
CLOCK_MONOTONIC 355.5M 359.6M +1%
CLOCK_REALTIME 355.5M 359.6M +1%
Cc: Thomas Gleixner <[email protected]>
Cc: Jason Vas Dias <[email protected]>
Suggested-by: Andy Lutomirski <[email protected]>
Signed-off-by: Alexander Sverdlin <[email protected]>
---
arch/x86/entry/vdso/vclock_gettime.c | 4 ++--
arch/x86/entry/vsyscall/vsyscall_gtod.c | 8 ++++++--
arch/x86/include/asm/vgtod.h | 4 ++--
3 files changed, 10 insertions(+), 6 deletions(-)
diff --git a/arch/x86/entry/vdso/vclock_gettime.c
b/arch/x86/entry/vdso/vclock_gettime.c
index 0f82a70..a99eaf5 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -153,8 +153,8 @@ notrace static int do_hres(clockid_t clk, struct timespec
*ts)
if (unlikely((s64)cycles < 0))
return vdso_fallback_gettime(clk, ts);
if (cycles > last)
- ns += (cycles - last) * gtod->mult;
- ns >>= gtod->shift;
+ ns += (cycles - last) * base->mult;
+ ns >>= base->shift;
sec = base->sec;
} while (unlikely(gtod_read_retry(gtod, seq)));
diff --git a/arch/x86/entry/vsyscall/vsyscall_gtod.c
b/arch/x86/entry/vsyscall/vsyscall_gtod.c
index cfcdba0..64b1e7c 100644
--- a/arch/x86/entry/vsyscall/vsyscall_gtod.c
+++ b/arch/x86/entry/vsyscall/vsyscall_gtod.c
@@ -44,16 +44,18 @@ void update_vsyscall(struct timekeeper *tk)
vdata->vclock_mode = vclock_mode;
vdata->cycle_last = tk->tkr_mono.cycle_last;
vdata->mask = tk->tkr_mono.mask;
- vdata->mult = tk->tkr_mono.mult;
- vdata->shift = tk->tkr_mono.shift;
base = &vdata->basetime[CLOCK_REALTIME];
base->sec = tk->xtime_sec;
base->nsec = tk->tkr_mono.xtime_nsec;
+ base->mult = tk->tkr_mono.mult;
+ base->shift = tk->tkr_mono.shift;
base = &vdata->basetime[CLOCK_TAI];
base->sec = tk->xtime_sec + (s64)tk->tai_offset;
base->nsec = tk->tkr_mono.xtime_nsec;
+ base->mult = tk->tkr_mono.mult;
+ base->shift = tk->tkr_mono.shift;
base = &vdata->basetime[CLOCK_MONOTONIC];
base->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
@@ -64,6 +66,8 @@ void update_vsyscall(struct timekeeper *tk)
base->sec++;
}
base->nsec = nsec;
+ base->mult = tk->tkr_mono.mult;
+ base->shift = tk->tkr_mono.shift;
base = &vdata->basetime[CLOCK_REALTIME_COARSE];
base->sec = tk->xtime_sec;
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h
index 913a133..b1f6df3 100644
--- a/arch/x86/include/asm/vgtod.h
+++ b/arch/x86/include/asm/vgtod.h
@@ -25,6 +25,8 @@ typedef unsigned long gtod_long_t;
struct vgtod_ts {
u64 sec;
u64 nsec;
+ u32 mult;
+ u32 shift;
};
#define VGTOD_BASES (CLOCK_TAI + 1)
@@ -41,8 +43,6 @@ struct vsyscall_gtod_data {
int vclock_mode;
u64 cycle_last;
u64 mask;
- u32 mult;
- u32 shift;
struct vgtod_ts basetime[VGTOD_BASES];
--
2.4.6
