From b21a0f95e76b285a0bc11b21eb347e8e0bf8dcf3 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 17 Sep 2018 14:45:41 +0200 Subject: [PATCH] x86/vdso: Replace the clockid switch case 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 Acked-by: Andy Lutomirski Cc: Peter Zijlstra Cc: Matt Rickard Cc: Stephen Boyd Cc: John Stultz Cc: Florian Weimer Cc: "K. Y. Srinivasan" Cc: Vitaly Kuznetsov Cc: devel@linuxdriverproject.org Cc: virtualization@lists.linux-foundation.org Cc: Paolo Bonzini Cc: Arnd Bergmann Cc: Juergen Gross Link: https://lkml.kernel.org/r/20180917130707.574315796@linutronix.de --- arch/x86/entry/vdso/vclock_gettime.c | 38 +++++++++++++--------------- 1 file changed, 18 insertions(+), 20 deletions(-) diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c index b27dea0e23af0..672e50e35d6c2 100644 --- a/arch/x86/entry/vdso/vclock_gettime.c +++ b/arch/x86/entry/vdso/vclock_gettime.c @@ -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"))); -- 2.39.5