Re: [PATCH] time/sched_clock: Use raw_read_seqcount_latch()
Hi Peter, Ahemd,
On Wed, Jul 15, 2020 at 05:58:50PM +0200, Peter Zijlstra wrote:
[...]
> > > diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
> > > index fa3f800d7d76..ea007928d681 100644
> > > --- a/kernel/time/sched_clock.c
> > > +++ b/kernel/time/sched_clock.c
> > > @@ -100,7 +100,7 @@ unsigned long long notrace sched_clock(void)
> > > struct clock_read_data *rd;
> > >
> > > do {
> > > - seq = raw_read_seqcount();
> > > + seq = raw_read_seqcount_latch();
> >
> > Understand this is doing the same thing with __ktime_get_fast_ns() and
> > I saw Peter acked to make change for this.
> >
> > Just want to confirm, since this patch introduces conflict with the
> > patch set "arm64: perf: Proper cap_user_time* support" [1], I should
> > rebase the patch set on top of this patch, right?
>
> Or rebase this patch on top of yours and include it, either way.
Have rebased this patch and included it in the patch set v3 for
"arm64: perf: Proper cap_user_time* support" [1].
Thanks!
Leo
[1]
https://lore.kernel.org/linux-arm-kernel/20200716051130.4359-3-leo@linaro.org/T/#u
Re: [PATCH] time/sched_clock: Use raw_read_seqcount_latch()
On Wed, Jul 15, 2020 at 11:29:26PM +0800, Leo Yan wrote:
> Hi Peter, Ahmed,
>
> On Wed, Jul 15, 2020 at 01:59:01PM +0200, Ahmed S. Darwish wrote:
> > sched_clock uses seqcount_t latching to switch between two storage
> > places protected by the sequence counter. This allows it to have
> > interruptible, NMI-safe, seqcount_t write side critical sections.
> >
> > Since 7fc26327b756 ("seqlock: Introduce raw_read_seqcount_latch()"),
> > raw_read_seqcount_latch() became the standardized way for seqcount_t
> > latch read paths. Due to the dependent load, it also has one read
> > memory barrier less than the currently used raw_read_seqcount() API.
> >
> > Use raw_read_seqcount_latch() for the seqcount_t latch read path.
> >
> > Link:
> > https://lkml.kernel.org/r/20200625085745.gd117...@hirez.programming.kicks-ass.net
> > Link:
> > https://lkml.kernel.org/r/20200715092345.ga231...@debian-buster-darwi.lab.linutronix.de
> > References: 1809bfa44e10 ("timers, sched/clock: Avoid deadlock during read
> > from NMI")
> > Signed-off-by: Ahmed S. Darwish
> > ---
> > kernel/time/sched_clock.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
> > index fa3f800d7d76..ea007928d681 100644
> > --- a/kernel/time/sched_clock.c
> > +++ b/kernel/time/sched_clock.c
> > @@ -100,7 +100,7 @@ unsigned long long notrace sched_clock(void)
> > struct clock_read_data *rd;
> >
> > do {
> > - seq = raw_read_seqcount();
> > + seq = raw_read_seqcount_latch();
>
> Understand this is doing the same thing with __ktime_get_fast_ns() and
> I saw Peter acked to make change for this.
>
> Just want to confirm, since this patch introduces conflict with the
> patch set "arm64: perf: Proper cap_user_time* support" [1], I should
> rebase the patch set on top of this patch, right?
Or rebase this patch on top of yours and include it, either way.
Re: [PATCH] time/sched_clock: Use raw_read_seqcount_latch()
Hi Peter, Ahmed,
On Wed, Jul 15, 2020 at 01:59:01PM +0200, Ahmed S. Darwish wrote:
> sched_clock uses seqcount_t latching to switch between two storage
> places protected by the sequence counter. This allows it to have
> interruptible, NMI-safe, seqcount_t write side critical sections.
>
> Since 7fc26327b756 ("seqlock: Introduce raw_read_seqcount_latch()"),
> raw_read_seqcount_latch() became the standardized way for seqcount_t
> latch read paths. Due to the dependent load, it also has one read
> memory barrier less than the currently used raw_read_seqcount() API.
>
> Use raw_read_seqcount_latch() for the seqcount_t latch read path.
>
> Link:
> https://lkml.kernel.org/r/20200625085745.gd117...@hirez.programming.kicks-ass.net
> Link:
> https://lkml.kernel.org/r/20200715092345.ga231...@debian-buster-darwi.lab.linutronix.de
> References: 1809bfa44e10 ("timers, sched/clock: Avoid deadlock during read
> from NMI")
> Signed-off-by: Ahmed S. Darwish
> ---
> kernel/time/sched_clock.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
> index fa3f800d7d76..ea007928d681 100644
> --- a/kernel/time/sched_clock.c
> +++ b/kernel/time/sched_clock.c
> @@ -100,7 +100,7 @@ unsigned long long notrace sched_clock(void)
> struct clock_read_data *rd;
>
> do {
> - seq = raw_read_seqcount();
> + seq = raw_read_seqcount_latch();
Understand this is doing the same thing with __ktime_get_fast_ns() and
I saw Peter acked to make change for this.
Just want to confirm, since this patch introduces conflict with the
patch set "arm64: perf: Proper cap_user_time* support" [1], I should
rebase the patch set on top of this patch, right?
Thanks,
Leo
[1] https://patchwork.kernel.org/cover/11664031/
> rd = cd.read_data + (seq & 1);
>
> cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
> --
> 2.20.1
[PATCH] time/sched_clock: Use raw_read_seqcount_latch()
sched_clock uses seqcount_t latching to switch between two storage
places protected by the sequence counter. This allows it to have
interruptible, NMI-safe, seqcount_t write side critical sections.
Since 7fc26327b756 ("seqlock: Introduce raw_read_seqcount_latch()"),
raw_read_seqcount_latch() became the standardized way for seqcount_t
latch read paths. Due to the dependent load, it also has one read
memory barrier less than the currently used raw_read_seqcount() API.
Use raw_read_seqcount_latch() for the seqcount_t latch read path.
Link:
https://lkml.kernel.org/r/20200625085745.gd117...@hirez.programming.kicks-ass.net
Link:
https://lkml.kernel.org/r/20200715092345.ga231...@debian-buster-darwi.lab.linutronix.de
References: 1809bfa44e10 ("timers, sched/clock: Avoid deadlock during read from
NMI")
Signed-off-by: Ahmed S. Darwish
---
kernel/time/sched_clock.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index fa3f800d7d76..ea007928d681 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -100,7 +100,7 @@ unsigned long long notrace sched_clock(void)
struct clock_read_data *rd;
do {
- seq = raw_read_seqcount();
+ seq = raw_read_seqcount_latch();
rd = cd.read_data + (seq & 1);
cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
--
2.20.1
