Re: [PATCH v2 1/3] x86, sched: check for counters overflow in frequency invariant accounting

From: Peter Zijlstra <peterz@infradead.org>
To: Giovanni Gherdovich <ggherdovich@suse.cz>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@suse.de>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	x86@kernel.org, linux-pm@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Subject: Re: [PATCH v2 1/3] x86, sched: check for counters overflow in frequency invariant accounting
Date: Thu, 22 Oct 2020 14:30:44 +0200	[thread overview]
Message-ID: <20201022123044.GX2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1603369318.3162.21.camel@suse.cz>

On Thu, Oct 22, 2020 at 02:21:58PM +0200, Giovanni Gherdovich wrote:
> On Thu, 2020-10-22 at 10:46 +0200, Peter Zijlstra wrote:
> > On Sun, May 31, 2020 at 08:24:51PM +0200, Giovanni Gherdovich wrote:
> > 
> > Hi Giovanni!
> > 
> > > +error:
> > > +	pr_warn("Scheduler frequency invariance went wobbly, disabling!\n");
> > > +	schedule_work(&disable_freq_invariance_work);
> > > +}
> > 
> > I'm getting reports that we trigger this on resume. Would it make sense
> > to hook into tsc_{save,restore}_sched_clock_state() (or somewhere near
> > there) to reset the state (basically call init_counter_refs() again to
> > ensure we're not having to deal with crazy ?
> 
> Hello,
> 
> right, if the counters keep running while the machine is suspended then the
> current code thinks it's a runtime overflow. I'll prepare a patch to fix that,
> thanks for the heads-up and the hint.

Either keep running, get reset, get scrambled, everything is possible.

Thanks!