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x86/vdso: Replace the clockid switch case

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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@linutronix.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Matt Rickard <matt@softrans.com.au>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: devel@linuxdriverproject.org
Cc: virtualization@lists.linux-foundation.org
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Juergen Gross <jgross@suse.com>
Link: https://lkml.kernel.org/r/20180917130707.574315796@linutronix.de
This commit is contained in:
Thomas Gleixner 2018-09-17 14:45:41 +02:00
parent 6deec5bdef
commit f3e8393841
1 changed files with 18 additions and 20 deletions
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38
arch/x86/entry/vdso/vclock_gettime.c
View File

@ -241,29 +241,27 @@ notrace static void do_coarse(clockid_t clk, struct timespec *ts)
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;
return 0;
fallback:
/* Sort out negative (CPU/FD) and invalid clocks */
if (unlikely((unsigned int) clock >= MAX_CLOCKS))
return vdso_fallback_gettime(clock, ts);
/*
* 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")));