On Fri, Oct 30, 2015 at 12:46:39AM +0000, Hiroshi Shimamoto wrote:
> +++ b/kernel/sched/cputime.c
> @@ -786,6 +786,9 @@ cputime_t task_gtime(struct task_struct *t)
> unsigned int seq;
> cputime_t gtime;
>
> + if (!context_tracking_is_enabled())
> + return t->gtime;
> +
Yeah, not happy about that.. why do we have to touch context tracking
muck to find vtime state etc.
> do {
> seq = read_seqbegin(&t->vtime_seqlock);
>
> --
> 1.8.3.1
>
On Mon, Nov 02, 2015 at 05:13:51PM +0100, Peter Zijlstra wrote:
> On Fri, Oct 30, 2015 at 12:46:39AM +0000, Hiroshi Shimamoto wrote:
> > +++ b/kernel/sched/cputime.c
> > @@ -786,6 +786,9 @@ cputime_t task_gtime(struct task_struct *t)
> > unsigned int seq;
> > cputime_t gtime;
> >
> > + if (!context_tracking_is_enabled())
> > + return t->gtime;
> > +
>
> Yeah, not happy about that.. why do we have to touch context tracking
> muck to find vtime state etc.
That's right, this is because it is deemed to be a quick and non invasive fix
to be backported.
Then will come the more invasive but proper fix consisting in having
vtime_accounting_enabled() telling if vtime is running on any CPU and
vtime_accounting_cpu_enabled(). The first will be used for remote readers
(as in this patch) and the second for writers.
Since we are dealing with a regression, it's better to minimize the changes.
AFAICT, the regression got introduced in 2012:
6a61671bb2f3a1bd12cd17b8fca811a624782632
("cputime: Safely read cputime of full dynticks CPUs")
>
> > do {
> > seq = read_seqbegin(&t->vtime_seqlock);
> >
> > --
> > 1.8.3.1
> >
> Subject: Re: [PATCH v3 1/2] cputime: fix invalid gtime in proc
>
> On Mon, Nov 02, 2015 at 05:13:51PM +0100, Peter Zijlstra wrote:
> > On Fri, Oct 30, 2015 at 12:46:39AM +0000, Hiroshi Shimamoto wrote:
> > > +++ b/kernel/sched/cputime.c
> > > @@ -786,6 +786,9 @@ cputime_t task_gtime(struct task_struct *t)
> > > unsigned int seq;
> > > cputime_t gtime;
> > >
> > > + if (!context_tracking_is_enabled())
> > > + return t->gtime;
> > > +
> >
> > Yeah, not happy about that.. why do we have to touch context tracking
> > muck to find vtime state etc.
>
> That's right, this is because it is deemed to be a quick and non invasive fix
> to be backported.
>
> Then will come the more invasive but proper fix consisting in having
> vtime_accounting_enabled() telling if vtime is running on any CPU and
> vtime_accounting_cpu_enabled(). The first will be used for remote readers
> (as in this patch) and the second for writers.
>
> Since we are dealing with a regression, it's better to minimize the changes.
> AFAICT, the regression got introduced in 2012:
>
> 6a61671bb2f3a1bd12cd17b8fca811a624782632
> ("cputime: Safely read cputime of full dynticks CPUs")
Is this patch going to apply to fix the regression?
thanks,
Hiroshi
>
> >
> > > do {
> > > seq = read_seqbegin(&t->vtime_seqlock);
> > >
> > > --
> > > 1.8.3.1
> > >
On Tue, Nov 10, 2015 at 08:43:17AM +0000, Hiroshi Shimamoto wrote:
> > Subject: Re: [PATCH v3 1/2] cputime: fix invalid gtime in proc
> >
> > On Mon, Nov 02, 2015 at 05:13:51PM +0100, Peter Zijlstra wrote:
> > > On Fri, Oct 30, 2015 at 12:46:39AM +0000, Hiroshi Shimamoto wrote:
> > > > +++ b/kernel/sched/cputime.c
> > > > @@ -786,6 +786,9 @@ cputime_t task_gtime(struct task_struct *t)
> > > > unsigned int seq;
> > > > cputime_t gtime;
> > > >
> > > > + if (!context_tracking_is_enabled())
> > > > + return t->gtime;
> > > > +
> > >
> > > Yeah, not happy about that.. why do we have to touch context tracking
> > > muck to find vtime state etc.
> >
> > That's right, this is because it is deemed to be a quick and non invasive fix
> > to be backported.
> >
> > Then will come the more invasive but proper fix consisting in having
> > vtime_accounting_enabled() telling if vtime is running on any CPU and
> > vtime_accounting_cpu_enabled(). The first will be used for remote readers
> > (as in this patch) and the second for writers.
> >
> > Since we are dealing with a regression, it's better to minimize the changes.
> > AFAICT, the regression got introduced in 2012:
> >
> > 6a61671bb2f3a1bd12cd17b8fca811a624782632
> > ("cputime: Safely read cputime of full dynticks CPUs")
>
> Is this patch going to apply to fix the regression?
Peter, if you have doubts, I can integrate this change in a larger
series that does a proper cleanup. But this very patch will still need
to be tagged as stable for backport.
Thanks.
On Fri, Nov 13, 2015 at 04:33:01PM +0100, Frederic Weisbecker wrote:
> Peter, if you have doubts, I can integrate this change in a larger
> series that does a proper cleanup. But this very patch will still need
> to be tagged as stable for backport.
Yeah, I want to see it done proper. I really do not care about backports
much.
Thanks!
On Fri, Nov 13, 2015 at 05:10:28PM +0100, Peter Zijlstra wrote:
> On Fri, Nov 13, 2015 at 04:33:01PM +0100, Frederic Weisbecker wrote:
> > Peter, if you have doubts, I can integrate this change in a larger
> > series that does a proper cleanup. But this very patch will still need
> > to be tagged as stable for backport.
>
> Yeah, I want to see it done proper. I really do not care about backports
> much.
Ok, I'll post something soon.
Thanks.