From: tip-bot for Thomas Gleixner <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: pbonzini@redhat.com, vkuznets@redhat.com,
linux-kernel@vger.kernel.org, jgross@suse.com,
matt@softrans.com.au, mingo@kernel.org, fweimer@redhat.com,
arnd@arndb.de, hpa@zytor.com, sboyd@kernel.org,
kys@microsoft.com, tglx@linutronix.de, john.stultz@linaro.org,
peterz@infradead.org, luto@kernel.org
Subject: [tip:x86/vdso] x86/vdso: Move cycle_last handling into the caller
Date: Thu, 4 Oct 2018 14:09:04 -0700 [thread overview]
Message-ID: <tip-3e89bf35ebf59c12e8c1476f6681fae0ebdcb2a7@git.kernel.org> (raw)
In-Reply-To: <20180917130707.741440803@linutronix.de>
Commit-ID: 3e89bf35ebf59c12e8c1476f6681fae0ebdcb2a7
Gitweb: https://git.kernel.org/tip/3e89bf35ebf59c12e8c1476f6681fae0ebdcb2a7
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Mon, 17 Sep 2018 14:45:43 +0200
Committer: Thomas Gleixner <tglx@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 <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/20180917130707.741440803@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)));
next prev parent reply other threads:[~2018-10-04 21:09 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-17 12:45 [patch V2 00/11] x86/vdso: Cleanups, simmplifications and CLOCK_TAI support Thomas Gleixner
2018-09-17 12:45 ` [patch V2 01/11] clocksource: Provide clocksource_arch_init() Thomas Gleixner
2018-09-17 20:05 ` John Stultz
2018-10-04 21:03 ` [tip:x86/vdso] " tip-bot for Thomas Gleixner
2018-09-17 12:45 ` [patch V2 02/11] x86/time: Implement clocksource_arch_init() Thomas Gleixner
2018-10-04 21:04 ` [tip:x86/vdso] " tip-bot for Thomas Gleixner
2018-09-17 12:45 ` [patch V2 03/11] x86/vdso: Enforce 64bit clocksource Thomas Gleixner
2018-10-04 21:05 ` [tip:x86/vdso] " tip-bot for Thomas Gleixner
2018-09-17 12:45 ` [patch V2 04/11] x86/vdso: Use unsigned int consistently for vsyscall_gtod_data::seq Thomas Gleixner
2018-10-04 21:05 ` [tip:x86/vdso] x86/vdso: Use unsigned int consistently for vsyscall_gtod_data:: Seq tip-bot for Thomas Gleixner
2018-09-17 12:45 ` [patch V2 05/11] x86/vdso: Introduce and use vgtod_ts Thomas Gleixner
2018-10-04 21:06 ` [tip:x86/vdso] " tip-bot for Thomas Gleixner
2018-09-17 12:45 ` [patch V2 06/11] x86/vdso: Collapse high resolution functions Thomas Gleixner
2018-10-04 21:06 ` [tip:x86/vdso] " tip-bot for Thomas Gleixner
2018-09-17 12:45 ` [patch V2 07/11] x86/vdso: Collapse coarse functions Thomas Gleixner
2018-10-04 21:07 ` [tip:x86/vdso] " tip-bot for Thomas Gleixner
2018-09-17 12:45 ` [patch V2 08/11] x86/vdso: Replace the clockid switch case Thomas Gleixner
2018-10-04 21:07 ` [tip:x86/vdso] " tip-bot for Thomas Gleixner
2018-09-17 12:45 ` [patch V2 09/11] x86/vdso: Simplify the invalid vclock case Thomas Gleixner
2018-10-04 21:08 ` [tip:x86/vdso] " tip-bot for Thomas Gleixner
2018-09-17 12:45 ` [patch V2 10/11] x86/vdso: Move cycle_last handling into the caller Thomas Gleixner
2018-10-04 21:09 ` tip-bot for Thomas Gleixner [this message]
2018-09-17 12:45 ` [patch V2 11/11] x66/vdso: Add CLOCK_TAI support Thomas Gleixner
2018-09-30 2:56 ` Matthew Rickard
2018-10-04 21:09 ` [tip:x86/vdso] " tip-bot for Thomas Gleixner
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