Messages in this thread | | | Date | Wed, 4 Nov 2015 17:14:57 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v3 1/2] cputime: fix invalid gtime in proc |
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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 > >
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