Now that the time getter functions use the clockid as index into the
storage array for the base time access, the switch case can be replaced.
- Check for clockid >= MAX_CLOCKS and for negative clockid (CPU/FD) first
and call the fallback function right away.
- After establishing that clockid is < MAX_CLOCKS, convert the clockid to a
bitmask
- Check for the supported high resolution and coarse functions by anding
the bitmask of supported clocks and check whether a bit is set.
This completely avoids jump tables, reduces the number of conditionals and
makes the VDSO extensible for other clock ids.
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/x86/entry/vdso/vclock_gettime.c | 38 ++++++++++++++++-------------------
1 file changed, 18 insertions(+), 20 deletions(-)
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -239,29 +239,27 @@ notrace static void do_coarse(clockid_t
notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
- switch (clock) {
- case CLOCK_REALTIME:
- if (do_hres(CLOCK_REALTIME, ts) == VCLOCK_NONE)
- goto fallback;
- break;
- case CLOCK_MONOTONIC:
- if (do_hres(CLOCK_MONOTONIC, ts) == VCLOCK_NONE)
- goto fallback;
- break;
- case CLOCK_REALTIME_COARSE:
- do_coarse(CLOCK_REALTIME_COARSE, ts);
- break;
- case CLOCK_MONOTONIC_COARSE:
- do_coarse(CLOCK_MONOTONIC_COARSE, ts);
- break;
- default:
- goto fallback;
- }
+ unsigned int msk;
+
+ /* Sort out negative (CPU/FD) and invalid clocks */
+ if (unlikely((unsigned int) clock >= MAX_CLOCKS))
+ return vdso_fallback_gettime(clock, ts);
- return 0;
-fallback:
+ /*
+ * Convert the clockid to a bitmask and use it to check which
+ * clocks are handled in the VDSO directly.
+ */
+ msk = 1U << clock;
+ if (likely(msk & VGTOD_HRES)) {
+ if (do_hres(clock, ts) != VCLOCK_NONE)
+ return 0;
+ } else if (msk & VGTOD_COARSE) {
+ do_coarse(clock, ts);
+ return 0;
+ }
return vdso_fallback_gettime(clock, ts);
}
+
int clock_gettime(clockid_t, struct timespec *)
__attribute__((weak, alias("__vdso_clock_gettime")));
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
