linux-kernel - Re: [PATCH V2 2/3] perf/x86/intel/bm.c: Add Intel Branch Monitoring support

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Date:   Tue, 12 Dec 2017 15:08:00 -0800
From:   Megha Dey <megha.dey@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, andriy.shevchenko@...ux.intel.com,
        kstewart@...uxfoundation.org, yu-cheng.yu@...el.com,
        len.brown@...el.com, gregkh@...uxfoundation.org, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, vikas.shivappa@...ux.intel.com,
        pombredanne@...b.com, me@...ehuey.com, bp@...e.de,
        grzegorz.andrejczuk@...el.com, tony.luck@...el.com, corbet@....net,
        ravi.v.shankar@...el.com
Subject: Re: [PATCH V2 2/3] perf/x86/intel/bm.c: Add Intel Branch Monitoring
 support

On Tue, 2017-12-12 at 23:32 +0100, Peter Zijlstra wrote:
> On Tue, Dec 12, 2017 at 01:10:57PM -0800, Megha Dey wrote:
> > On Mon, 2017-11-20 at 12:57 +0100, Peter Zijlstra wrote:
> > > On Fri, Nov 17, 2017 at 05:54:05PM -0800, Megha Dey wrote:
> > > > +	mutex_lock(&bm_counter_mutex);
> > > > +	for (i = 0; i < BM_MAX_COUNTERS; i++) {
> > > > +		if (bm_counter_owner[i] == NULL) {
> > > > +			counter_to_use = i;
> > > > +			bm_counter_owner[i] = event;
> > > > +			break;
> > > > +		}
> > > > +	}
> > > > +	mutex_unlock(&bm_counter_mutex);
> > > > +
> > > > +	if (counter_to_use == -1)
> > > > +		return -EBUSY;
> > > 
> > > > +static struct pmu intel_bm_pmu = {
> > > > +	.task_ctx_nr     = perf_sw_context,
> > > > +	.attr_groups     = intel_bm_attr_groups,
> > > > +	.event_init      = intel_bm_event_init,
> > > > +	.add             = intel_bm_event_add,
> > > > +	.del             = intel_bm_event_del,
> > > > +};
> > > 
> > > Still horrid.. still no.
> > 
> > It seems like perf_invalid_context does not support per task monitoring:
> > find_get_context():
> >  ctxn = pmu->task_ctx_nr;
> >         if (ctxn < 0)
> >                 goto errout;
> > 
> > Also, perf_hw_context is to be used only for core PMU, correct?
> > 
> > That leaves us with only perf_sw_context to be used. Not sure if a new
> > context needs to be implemented.
> 
> There's work on the way to allow multiple HW PMUs. You'll either have to
> wait for that or help in making that happen. What you do not do is
> silently hack around it.

Could I get a pointer to the code implementing this?

I assume that this patch cannot be accepted until there is a way to
allow multiple HW PMUs even if appropriate comments are added?