linux-kernel - RE: [patch 04/11] x86/perf/intel_uncore: Cleanup hardware on exit

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Message-ID: <alpine.DEB.2.11.1602171858000.19512@nanos>
Date:	Wed, 17 Feb 2016 19:16:54 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Liang, Kan" <kan.liang@...el.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Stephane Eranian <eranian@...gle.com>,
	"Chegondi, Harish" <harish.chegondi@...el.com>,
	"Kleen, Andi" <andi.kleen@...el.com>
Subject: RE: [patch 04/11] x86/perf/intel_uncore: Cleanup hardware on exit

On Wed, 17 Feb 2016, Liang, Kan wrote:
> > When tearing down the boxes nothing undoes the hardware state which
> > was setup by box->init_box(). Add a box->exit_box() callback and
> > implement it for the uncores which have an init_box() callback.
> 
> I don't think we need exit_box.
> Because in disable_box we already freezes the box.

init_box() != enable_box() 
exit_box() != disable_box()

And we certainly want to clear stuff which enables things at a different
msr/config word location than what you do with the enable/disable callbacks.

I'm not a fan of leaving hardware in some random state.

> Also, writing 0 cannot clear hardware state. It will unfreeze the box.
> The counter will start to count.

Nonsense.
 
> > @@ -201,6 +201,11 @@ static void nhmex_uncore_msr_init_box(st
> >  	wrmsrl(NHMEX_U_MSR_PMON_GLOBAL_CTL,
> > NHMEX_U_PMON_GLOBAL_EN_ALL);  }

> > +static void nhmex_uncore_msr_exit_box(struct intel_uncore_box *box)
> > {
> > +	wrmsrl(NHMEX_U_MSR_PMON_GLOBAL_CTL, 0); }

The reset value for this register is 0. So how is that wrong?

> > +static void snb_uncore_msr_exit_box(struct intel_uncore_box *box) {
> > +	if (box->pmu->pmu_idx == 0)
> > +		wrmsrl(SNB_UNC_PERF_GLOBAL_CTL, 0);
> > +}

Ditto.

> > +static void snb_uncore_imc_exit_box(struct intel_uncore_box *box) {
> > +	iounmap(box->io_addr);

That's definitely required, because it would leak a mapping.

I know Intel folks do not care about error handling and a few reference leaks,
but I care very much.

If there is a single instance of exit_box() in that patch which flips the
wrong bits, then please point it out with the proper reference in the manual
and not with such half baken statements as above.

Thanks,

	tglx