| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <3715iro0.fsf@gmail.com>
Date: Mon, 12 Mar 2018 09:12:15 +0000
From: Jason Vas Dias <jason.vas.dias@...il.com>
To: x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
andi <andi@...stfloor.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v4.16-rc4 1/2] x86/vdso: on Intel, VDSO should handle CLOCK_MONOTONIC_RAW
Currently the VDSO does not handle
clock_gettime( CLOCK_MONOTONIC_RAW, &ts )
on Intel / AMD - it calls
vdso_fallback_gettime()
for this clock, which issues a syscall, having an unacceptably high
latency (minimum measurable time or time between measurements)
of 300-700ns on 2 2.8-3.9ghz Haswell x86_64 Family'_'Model : 06_3C
machines under various versions of Linux.
Sometimes, particularly when correlating elapsed time to performance
counter values, code needs to know elapsed time from the perspective
of the CPU no matter how "hot" / fast or "cold" / slow it might be
running wrt NTP / PTP ; when code needs this, the latencies with
a syscall are often unacceptably high.
I reported this as Bug #198161 :
'https://bugzilla.kernel.org/show_bug.cgi?id=198961'
and in previous posts with subjects matching 'CLOCK_MONOTONIC_RAW' .
This patch handles CLOCK_MONOTONIC_RAW clock_gettime() in the VDSO ,
by exporting the raw clock calibration, last cycles, last xtime_nsec,
and last raw_sec value in the vsyscall_gtod_data during vsyscall_update() .
Now the new do_monotonic_raw() function in the vDSO has a latency of @ 24ns
on average, and the test program:
tools/testing/selftest/timers/inconsistency-check.c
succeeds with arguments: '-c 4 -t 120' or any arbitrary -t value.
The patch is against Linus' latest 4.16-rc5 tree,
current HEAD of :
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
.
This patch affects only these files:
arch/x86/include/asm/vgtod.h
arch/x86/entry/vdso/vclock_gettime.c
arch/x86/entry/vsyscall/vsyscall_gtod.c
There are 2 patches in the series - this first
one handles CLOCK_MONOTONIC_RAW in VDSO using
existing rdtsc_ordered() , and the second
uses new rstscp() function which avoids
use of an explicit barrier.
Best Regards,
Jason Vas Dias .
---
diff -up linux-4.16-rc5.1/arch/x86/entry/vdso/vclock_gettime.c.4.16-rc5 linux-4.16-rc5.1/arch/x86/entry/vdso/vclock_gettime.c
--- linux-4.16-rc5.1/arch/x86/entry/vdso/vclock_gettime.c.4.16-rc5 2018-03-12 00:25:09.000000000 +0000
+++ linux-4.16-rc5.1/arch/x86/entry/vdso/vclock_gettime.c 2018-03-12 08:12:17.110120433 +0000
@@ -182,6 +182,18 @@ notrace static u64 vread_tsc(void)
return last;
}
+notrace static u64 vread_tsc_raw(void)
+{
+ u64 tsc
+ , last = gtod->raw_cycle_last;
+
+ tsc = rdtsc_ordered();
+ if (likely(tsc >= last))
+ return tsc;
+ asm volatile ("");
+ return last;
+}
+
notrace static inline u64 vgetsns(int *mode)
{
u64 v;
@@ -203,6 +215,27 @@ notrace static inline u64 vgetsns(int *m
return v * gtod->mult;
}
+notrace static inline u64 vgetsns_raw(int *mode)
+{
+ u64 v;
+ cycles_t cycles;
+
+ if (gtod->vclock_mode == VCLOCK_TSC)
+ cycles = vread_tsc_raw();
+#ifdef CONFIG_PARAVIRT_CLOCK
+ else if (gtod->vclock_mode == VCLOCK_PVCLOCK)
+ cycles = vread_pvclock(mode);
+#endif
+#ifdef CONFIG_HYPERV_TSCPAGE
+ else if (gtod->vclock_mode == VCLOCK_HVCLOCK)
+ cycles = vread_hvclock(mode);
+#endif
+ else
+ return 0;
+ v = (cycles - gtod->raw_cycle_last) & gtod->raw_mask;
+ return v * gtod->raw_mult;
+}
+
/* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
notrace static int __always_inline do_realtime(struct timespec *ts)
{
@@ -246,6 +279,27 @@ notrace static int __always_inline do_mo
return mode;
}
+notrace static __always_inline 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 void do_realtime_coarse(struct timespec *ts)
{
unsigned long seq;
@@ -277,6 +331,10 @@ notrace int __vdso_clock_gettime(clockid
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 -up linux-4.16-rc5.1/arch/x86/entry/vsyscall/vsyscall_gtod.c.4.16-rc5 linux-4.16-rc5.1/arch/x86/entry/vsyscall/vsyscall_gtod.c
--- linux-4.16-rc5.1/arch/x86/entry/vsyscall/vsyscall_gtod.c.4.16-rc5 2018-03-12 00:25:09.000000000 +0000
+++ linux-4.16-rc5.1/arch/x86/entry/vsyscall/vsyscall_gtod.c 2018-03-12 07:58:07.974214168 +0000
@@ -45,6 +45,11 @@ void update_vsyscall(struct timekeeper *
vdata->mult = tk->tkr_mono.mult;
vdata->shift = tk->tkr_mono.shift;
+ vdata->raw_cycle_last = tk->tkr_raw.cycle_last;
+ vdata->raw_mask = tk->tkr_raw.mask;
+ 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 +79,8 @@ void update_vsyscall(struct timekeeper *
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);
}
--- linux-4.16-rc5.1/arch/x86/include/asm/vgtod.h.4.16-rc5 2018-03-12 00:25:09.000000000 +0000
+++ linux-4.16-rc5.1/arch/x86/include/asm/vgtod.h 2018-03-12 07:44:17.910539760 +0000
@@ -22,6 +22,10 @@ struct vsyscall_gtod_data {
u64 mask;
u32 mult;
u32 shift;
+ u64 raw_cycle_last;
+ u64 raw_mask;
+ u32 raw_mult;
+ u32 raw_shift;
/* open coded 'struct timespec' */
u64 wall_time_snsec;
@@ -32,6 +36,8 @@ 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;
---
Powered by blists - more mailing lists