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Date: Mon, 19 Mar 2018 17:04:01 +0000
From: jason.vas.dias@...il.com
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, tglx@...utronix.de, mingo@...nel.org,
peterz@...radead.org, andi@...stfloor.org
Subject: [PATCH v4.16-rc6 1/1] x86/vdso: VDSO should handle clock_gettime(CLOCK_MONOTONIC_RAW) without syscall
This patch makes the vDSO handle clock_gettime(CLOCK_MONOTONIC_RAW,&ts)
calls in the same way it handles clock_gettime(CLOCK_MONOTONIC,&ts) calls,
reducing latency from @ 200-1000ns to @ 20ns.
It has been resent and augmented to support compilation with -DRETPOLINE /
-mindirect-branch=thunk-extern -mindirect-branch-register, to avoid
generating relocations for thunks.
---
diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index f19856d..9b89f86 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -182,29 +182,60 @@ notrace static u64 vread_tsc(void)
return last;
}
-notrace static inline u64 vgetsns(int *mode)
+notrace static inline u64 vgetcycles(int *mode)
{
- u64 v;
- cycles_t cycles;
-
- if (gtod->vclock_mode == VCLOCK_TSC)
- cycles = vread_tsc();
+ switch (gtod->vclock_mode) {
+ case VCLOCK_TSC:
+ return vread_tsc();
#ifdef CONFIG_PARAVIRT_CLOCK
- else if (gtod->vclock_mode == VCLOCK_PVCLOCK)
- cycles = vread_pvclock(mode);
+ case VCLOCK_PVCLOCK:
+ return vread_pvclock(mode);
#endif
#ifdef CONFIG_HYPERV_TSCPAGE
- else if (gtod->vclock_mode == VCLOCK_HVCLOCK)
- cycles = vread_hvclock(mode);
+ case VCLOCK_HVCLOCK:
+ return vread_hvclock(mode);
#endif
- else
+ default:
+ break;
+ }
+ return 0;
+}
+
+notrace static inline u64 vgetsns(int *mode)
+{
+ u64 v;
+ cycles_t cycles = vgetcycles(mode);
+
+ if (cycles == 0)
return 0;
+
v = (cycles - gtod->cycle_last) & gtod->mask;
return v * gtod->mult;
}
+notrace static inline u64 vgetsns_raw(int *mode)
+{
+ u64 v;
+ cycles_t cycles = vgetcycles(mode);
+
+ if (cycles == 0)
+ return 0;
+
+ v = (cycles - gtod->cycle_last) & gtod->mask;
+ return v * gtod->raw_mult;
+}
+
+#ifdef RETPOLINE
+# define _NO_THUNK_RELOCS_()(indirect_branch("keep"),\
+ function_return("keep"))
+# define _RETPOLINE_FUNC_ATTR_ __attribute__(_NO_THUNK_RELOCS_())
+#else
+# define _RETPOLINE_FUNC_ATTR_
+#endif
+
/* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
-notrace static int __always_inline do_realtime(struct timespec *ts)
+notrace static inline _RETPOLINE_FUNC_ATTR_
+int do_realtime(struct timespec *ts)
{
unsigned long seq;
u64 ns;
@@ -225,7 +256,8 @@ notrace static int __always_inline do_realtime(struct timespec *ts)
return mode;
}
-notrace static int __always_inline do_monotonic(struct timespec *ts)
+notrace static inline _RETPOLINE_FUNC_ATTR_
+int do_monotonic(struct timespec *ts)
{
unsigned long seq;
u64 ns;
@@ -246,7 +278,30 @@ notrace static int __always_inline do_monotonic(struct timespec *ts)
return mode;
}
-notrace static void do_realtime_coarse(struct timespec *ts)
+notrace static inline _RETPOLINE_FUNC_ATTR_
+int do_monotonic_raw(struct timespec *ts)
+{
+ unsigned long seq;
+ u64 ns;
+ int mode;
+
+ do {
+ seq = gtod_read_begin(gtod);
+ mode = gtod->vclock_mode;
+ ts->tv_sec = gtod->monotonic_time_raw_sec;
+ ns = gtod->monotonic_time_raw_nsec;
+ ns += vgetsns_raw(&mode);
+ ns >>= gtod->raw_shift;
+ } while (unlikely(gtod_read_retry(gtod, seq)));
+
+ ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
+ ts->tv_nsec = ns;
+
+ return mode;
+}
+
+notrace static inline _RETPOLINE_FUNC_ATTR_
+void do_realtime_coarse(struct timespec *ts)
{
unsigned long seq;
do {
@@ -256,7 +311,8 @@ notrace static void do_realtime_coarse(struct timespec *ts)
} while (unlikely(gtod_read_retry(gtod, seq)));
}
-notrace static void do_monotonic_coarse(struct timespec *ts)
+notrace static inline _RETPOLINE_FUNC_ATTR_
+void do_monotonic_coarse(struct timespec *ts)
{
unsigned long seq;
do {
@@ -266,7 +322,11 @@ notrace static void do_monotonic_coarse(struct timespec *ts)
} while (unlikely(gtod_read_retry(gtod, seq)));
}
-notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
+notrace
+#ifdef RETPOLINE
+ __attribute__((indirect_branch("keep"), function_return("keep")))
+#endif
+int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
switch (clock) {
case CLOCK_REALTIME:
@@ -277,6 +337,10 @@ notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
if (do_monotonic(ts) == VCLOCK_NONE)
goto fallback;
break;
+ case CLOCK_MONOTONIC_RAW:
+ if (do_monotonic_raw(ts) == VCLOCK_NONE)
+ goto fallback;
+ break;
case CLOCK_REALTIME_COARSE:
do_realtime_coarse(ts);
break;
diff --git a/arch/x86/entry/vsyscall/vsyscall_gtod.c b/arch/x86/entry/vsyscall/vsyscall_gtod.c
index e1216dd..c4d89b6 100644
--- a/arch/x86/entry/vsyscall/vsyscall_gtod.c
+++ b/arch/x86/entry/vsyscall/vsyscall_gtod.c
@@ -44,6 +44,8 @@ void update_vsyscall(struct timekeeper *tk)
vdata->mask = tk->tkr_mono.mask;
vdata->mult = tk->tkr_mono.mult;
vdata->shift = tk->tkr_mono.shift;
+ vdata->raw_mult = tk->tkr_raw.mult;
+ vdata->raw_shift = tk->tkr_raw.shift;
vdata->wall_time_sec = tk->xtime_sec;
vdata->wall_time_snsec = tk->tkr_mono.xtime_nsec;
@@ -74,5 +76,8 @@ void update_vsyscall(struct timekeeper *tk)
vdata->monotonic_time_coarse_sec++;
}
+ vdata->monotonic_time_raw_sec = tk->raw_sec;
+ vdata->monotonic_time_raw_nsec = tk->tkr_raw.xtime_nsec;
+
gtod_write_end(vdata);
}
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h
index fb856c9..ec1a37c 100644
--- a/arch/x86/include/asm/vgtod.h
+++ b/arch/x86/include/asm/vgtod.h
@@ -22,7 +22,8 @@ struct vsyscall_gtod_data {
u64 mask;
u32 mult;
u32 shift;
-
+ u32 raw_mult;
+ u32 raw_shift;
/* open coded 'struct timespec' */
u64 wall_time_snsec;
gtod_long_t wall_time_sec;
@@ -32,6 +33,8 @@ struct vsyscall_gtod_data {
gtod_long_t wall_time_coarse_nsec;
gtod_long_t monotonic_time_coarse_sec;
gtod_long_t monotonic_time_coarse_nsec;
+ gtod_long_t monotonic_time_raw_sec;
+ gtod_long_t monotonic_time_raw_nsec;
int tz_minuteswest;
int tz_dsttime;
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