Commit-ID: 3e89bf35ebf59c12e8c1476f6681fae0ebdcb2a7 Gitweb: https://git.kernel.org/tip/3e89bf35ebf59c12e8c1476f6681fae0ebdcb2a7 Author: Thomas Gleixner <t...@linutronix.de> AuthorDate: Mon, 17 Sep 2018 14:45:43 +0200 Committer: Thomas Gleixner <t...@linutronix.de> CommitDate: Thu, 4 Oct 2018 23:00:27 +0200
x86/vdso: Move cycle_last handling into the caller Dereferencing gtod->cycle_last all over the place and foing the cycles < last comparison in the vclock read functions generates horrible code. Doing it at the call site is much better and gains a few cycles both for TSC and pvclock. Caveat: This adds the comparison to the hyperv vclock as well, but I have no way to test that. Signed-off-by: Thomas Gleixner <t...@linutronix.de> Acked-by: Andy Lutomirski <l...@kernel.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Matt Rickard <m...@softrans.com.au> Cc: Stephen Boyd <sb...@kernel.org> Cc: John Stultz <john.stu...@linaro.org> Cc: Florian Weimer <fwei...@redhat.com> Cc: "K. Y. Srinivasan" <k...@microsoft.com> Cc: Vitaly Kuznetsov <vkuzn...@redhat.com> Cc: de...@linuxdriverproject.org Cc: virtualizat...@lists.linux-foundation.org Cc: Paolo Bonzini <pbonz...@redhat.com> Cc: Arnd Bergmann <a...@arndb.de> Cc: Juergen Gross <jgr...@suse.com> Link: https://lkml.kernel.org/r/20180917130707.741440...@linutronix.de --- arch/x86/entry/vdso/vclock_gettime.c | 39 +++++++----------------------------- 1 file changed, 7 insertions(+), 32 deletions(-) diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c index 40105024a210..b7ccbff26a3f 100644 --- a/arch/x86/entry/vdso/vclock_gettime.c +++ b/arch/x86/entry/vdso/vclock_gettime.c @@ -77,9 +77,8 @@ static notrace const struct pvclock_vsyscall_time_info *get_pvti0(void) static notrace u64 vread_pvclock(void) { const struct pvclock_vcpu_time_info *pvti = &get_pvti0()->pvti; - u64 ret; - u64 last; u32 version; + u64 ret; /* * Note: The kernel and hypervisor must guarantee that cpu ID @@ -112,13 +111,7 @@ static notrace u64 vread_pvclock(void) ret = __pvclock_read_cycles(pvti, rdtsc_ordered()); } while (pvclock_read_retry(pvti, version)); - /* refer to vread_tsc() comment for rationale */ - last = gtod->cycle_last; - - if (likely(ret >= last)) - return ret; - - return last; + return ret; } #endif #ifdef CONFIG_HYPERV_TSCPAGE @@ -131,30 +124,10 @@ static notrace u64 vread_hvclock(void) } #endif -notrace static u64 vread_tsc(void) -{ - u64 ret = (u64)rdtsc_ordered(); - u64 last = gtod->cycle_last; - - if (likely(ret >= last)) - return ret; - - /* - * GCC likes to generate cmov here, but this branch is extremely - * predictable (it's just a function of time and the likely is - * very likely) and there's a data dependence, so force GCC - * to generate a branch instead. I don't barrier() because - * we don't actually need a barrier, and if this function - * ever gets inlined it will generate worse code. - */ - asm volatile (""); - return last; -} - notrace static inline u64 vgetcyc(int mode) { if (mode == VCLOCK_TSC) - return vread_tsc(); + return (u64)rdtsc_ordered(); #ifdef CONFIG_PARAVIRT_CLOCK else if (mode == VCLOCK_PVCLOCK) return vread_pvclock(); @@ -169,17 +142,19 @@ notrace static inline u64 vgetcyc(int mode) notrace static int do_hres(clockid_t clk, struct timespec *ts) { struct vgtod_ts *base = >od->basetime[clk]; + u64 cycles, last, ns; unsigned int seq; - u64 cycles, ns; do { seq = gtod_read_begin(gtod); ts->tv_sec = base->sec; ns = base->nsec; + last = gtod->cycle_last; cycles = vgetcyc(gtod->vclock_mode); if (unlikely((s64)cycles < 0)) return vdso_fallback_gettime(clk, ts); - ns += (cycles - gtod->cycle_last) * gtod->mult; + if (cycles > last) + ns += (cycles - last) * gtod->mult; ns >>= gtod->shift; } while (unlikely(gtod_read_retry(gtod, seq)));
