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Date: Tue, 17 Nov 2009 13:58:41 +0800
From: Lin Ming <ming.m.lin@...el.com>
To: tglx@...utronix.de
Cc: schwidefsky@...ibm.com, mingo@...e.hu,
"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Fix clock_gettime vsyscall time warp
On Tue, 2009-11-17 at 13:49 +0800, Lin Ming wrote:
> Hi, all
>
> clock_gettime vsyscall time warp was seen on a x86_64 machine with 16
> logical cpus and an IA64 machine with 32 logical CPUS.
>
> time-warp-test was downloaded from
> http://people.redhat.com/mingo/time-warp-test/
>
> I wrote a simple patch to port this test tool to non-x86 platform.
> See the attachment time-warp-test.non-x86.patch.
Forgot the attachment.
Attached.
Lin Ming
>
> [x86_64]$ ./time-warp-test 4
> 16 CPUs, running 4 parallel test-tasks.
> checking for time-warps via:
> - clock_gettime(CLOCK_MONOTONIC) syscall (nsec resolution)
>
> new CLOCK-warp maximum: -120 nsecs, 00000025c337c537 -> 00000025c337c4bf
> new CLOCK-warp maximum: -147 nsecs, 00000025e1052a7d -> 00000025e10529ea
> new CLOCK-warp maximum: -174 nsecs, 0000002693d58856 -> 0000002693d587a8
> new CLOCK-warp maximum: -176 nsecs, 000000270b0b1c41 -> 000000270b0b1b91
> new CLOCK-warp maximum: -206 nsecs, 0000002746a5e740 -> 0000002746a5e672
> new CLOCK-warp maximum: -209 nsecs, 000000295f170082 -> 000000295f16ffb1
> | CLK: 0.13us, fail:52 /
>
> [ia64]$ ./time-warp-test
> 32 CPUs, running 32 parallel test-tasks.
> checking for time-warps via:
> - clock_gettime(CLOCK_MONOTONIC) syscall (nsec resolution)
>
> new CLOCK-warp maximum: -54 nsecs, 0000001a8178a9c1 -> 0000001a8178a98b
> new CLOCK-warp maximum: -55 nsecs, 0000001a8d2769fe -> 0000001a8d2769c7
> | CLK: 2.60us, fail:5 |
>
> The root cause is the NTP adjusted clock multiplier(timekeeper.mult) is
> not updated to vsyscall gtod data(vsyscall_gtod_data.clock.mult).
>
> Since commit 0a544198 "timekeeping: Move NTP adjusted clock multiplier
> to struct timekeeper", clock->mult is only the unmodified multiplier.
>
> Below patch passes the adjusted clock multiplier to update_vsyscall.
> -void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
> +void update_vsyscall(struct timespec *wall_time, struct clocksource *clock, u32 mult)
>
> With this patch applied to 2.6.32-rc7, I have been running
> time-warp-test for many hours without any time warp on both x86_64 and
> ia64 machines.
>
> This patch also touches the powerpc code, so it would be very
> appreciated if anyone can help to test it on powerpc.
>
> Signed-off-by: Lin Ming <ming.m.lin@...el.com>
> ---
> arch/ia64/kernel/time.c | 4 ++--
> arch/powerpc/kernel/time.c | 4 ++--
> arch/s390/kernel/time.c | 2 +-
> arch/x86/kernel/vsyscall_64.c | 4 ++--
> include/linux/clocksource.h | 4 ++--
> kernel/time/timekeeping.c | 6 +++---
> 6 files changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/arch/ia64/kernel/time.c b/arch/ia64/kernel/time.c
> index 4990495..a35c661 100644
> --- a/arch/ia64/kernel/time.c
> +++ b/arch/ia64/kernel/time.c
> @@ -473,7 +473,7 @@ void update_vsyscall_tz(void)
> {
> }
>
> -void update_vsyscall(struct timespec *wall, struct clocksource *c)
> +void update_vsyscall(struct timespec *wall, struct clocksource *c, u32 mult)
> {
> unsigned long flags;
>
> @@ -481,7 +481,7 @@ void update_vsyscall(struct timespec *wall, struct clocksource *c)
>
> /* copy fsyscall clock data */
> fsyscall_gtod_data.clk_mask = c->mask;
> - fsyscall_gtod_data.clk_mult = c->mult;
> + fsyscall_gtod_data.clk_mult = mult;
> fsyscall_gtod_data.clk_shift = c->shift;
> fsyscall_gtod_data.clk_fsys_mmio = c->fsys_mmio;
> fsyscall_gtod_data.clk_cycle_last = c->cycle_last;
> diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
> index a136a11..ae4d55f 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -828,7 +828,7 @@ static cycle_t timebase_read(struct clocksource *cs)
> return (cycle_t)get_tb();
> }
>
> -void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
> +void update_vsyscall(struct timespec *wall_time, struct clocksource *clock, u32 mult)
> {
> u64 t2x, stamp_xsec;
>
> @@ -841,7 +841,7 @@ void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
>
> /* XXX this assumes clock->shift == 22 */
> /* 4611686018 ~= 2^(20+64-22) / 1e9 */
> - t2x = (u64) clock->mult * 4611686018ULL;
> + t2x = (u64) mult * 4611686018ULL;
> stamp_xsec = (u64) xtime.tv_nsec * XSEC_PER_SEC;
> do_div(stamp_xsec, 1000000000);
> stamp_xsec += (u64) xtime.tv_sec * XSEC_PER_SEC;
> diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
> index 34162a0..7b1a3a6 100644
> --- a/arch/s390/kernel/time.c
> +++ b/arch/s390/kernel/time.c
> @@ -214,7 +214,7 @@ struct clocksource * __init clocksource_default_clock(void)
> return &clocksource_tod;
> }
>
> -void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
> +void update_vsyscall(struct timespec *wall_time, struct clocksource *clock, u32 mult)
> {
> if (clock != &clocksource_tod)
> return;
> diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
> index 8cb4974..0d156eb 100644
> --- a/arch/x86/kernel/vsyscall_64.c
> +++ b/arch/x86/kernel/vsyscall_64.c
> @@ -73,7 +73,7 @@ void update_vsyscall_tz(void)
> write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
> }
>
> -void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
> +void update_vsyscall(struct timespec *wall_time, struct clocksource *clock, u32 mult)
> {
> unsigned long flags;
>
> @@ -82,7 +82,7 @@ void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
> vsyscall_gtod_data.clock.vread = clock->vread;
> vsyscall_gtod_data.clock.cycle_last = clock->cycle_last;
> vsyscall_gtod_data.clock.mask = clock->mask;
> - vsyscall_gtod_data.clock.mult = clock->mult;
> + vsyscall_gtod_data.clock.mult = mult;
> vsyscall_gtod_data.clock.shift = clock->shift;
> vsyscall_gtod_data.wall_time_sec = wall_time->tv_sec;
> vsyscall_gtod_data.wall_time_nsec = wall_time->tv_nsec;
> diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
> index 83d2fbd..b18e8a2 100644
> --- a/include/linux/clocksource.h
> +++ b/include/linux/clocksource.h
> @@ -280,10 +280,10 @@ extern struct clocksource * __init __weak clocksource_default_clock(void);
> extern void clocksource_mark_unstable(struct clocksource *cs);
>
> #ifdef CONFIG_GENERIC_TIME_VSYSCALL
> -extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
> +extern void update_vsyscall(struct timespec *ts, struct clocksource *c, u32 mult);
> extern void update_vsyscall_tz(void);
> #else
> -static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
> +static inline void update_vsyscall(struct timespec *ts, struct clocksource *c, u32 mult)
> {
> }
>
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index c3a4e29..2a6d3e3 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -177,7 +177,7 @@ void timekeeping_leap_insert(int leapsecond)
> {
> xtime.tv_sec += leapsecond;
> wall_to_monotonic.tv_sec -= leapsecond;
> - update_vsyscall(&xtime, timekeeper.clock);
> + update_vsyscall(&xtime, timekeeper.clock, timekeeper.mult);
> }
>
> #ifdef CONFIG_GENERIC_TIME
> @@ -337,7 +337,7 @@ int do_settimeofday(struct timespec *tv)
> timekeeper.ntp_error = 0;
> ntp_clear();
>
> - update_vsyscall(&xtime, timekeeper.clock);
> + update_vsyscall(&xtime, timekeeper.clock, timekeeper.mult);
>
> write_sequnlock_irqrestore(&xtime_lock, flags);
>
> @@ -811,7 +811,7 @@ void update_wall_time(void)
> update_xtime_cache(nsecs);
>
> /* check to see if there is a new clocksource to use */
> - update_vsyscall(&xtime, timekeeper.clock);
> + update_vsyscall(&xtime, timekeeper.clock, timekeeper.mult);
> }
>
> /**
>
View attachment "time-warp-test.non-x86.patch" of type "text/x-patch" (3187 bytes)
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