linux-kernel - Re: [PATCH V0 2/3] perf/x86/intel/bm.c: Add Intel Branch Monitoring support

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Message-ID: <20171104132459.GA8454@krava>
Date:   Sat, 4 Nov 2017 14:24:59 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Megha Dey <megha.dey@...ux.intel.com>
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,
        peterz@...radead.org, acme@...nel.org,
        alexander.shishkin@...ux.intel.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,
        megha.dey@...el.com
Subject: Re: [PATCH V0 2/3] perf/x86/intel/bm.c: Add Intel Branch Monitoring
 support

On Fri, Nov 03, 2017 at 11:00:05AM -0700, Megha Dey wrote:

SNIP

> +
> +static int intel_bm_event_nmi_handler(unsigned int cmd, struct pt_regs *regs)
> +{
> +	struct perf_event *event;
> +	union bm_detect_status stat;
> +	struct perf_sample_data data;
> +	int i;
> +	unsigned long x;
> +
> +	rdmsrl(BR_DETECT_STATUS_MSR, stat.raw);
> +
> +	if (stat.event) {
> +		wrmsrl(BR_DETECT_STATUS_MSR, 0);
> +		apic_write(APIC_LVTPC, APIC_DM_NMI);
> +		/*
> +		 * Issue wake-up to corrresponding polling event
> +		 */
> +		x = stat.ctrl_hit;
> +		for_each_set_bit(i, &x, bm_num_counters) {
> +			event = bm_counter_owner[i];
> +			perf_sample_data_init(&data, 0, event->hw.last_period);
> +			perf_event_overflow(event, &data, regs);

hum, it's non sampling events only right? then you don't need
any of the perf_sample_data stuff.. the perf_event_overflow call
is basicaly nop

> +			local64_inc(&event->count);
> +			atomic_set(&event->hw.bm_poll, POLLIN);
> +			event->pending_wakeup = 1;
> +			irq_work_queue(&event->pending);

also this is for sampling events only

seems like you only want to increment the event->count in here

thanks,
jirka

> +		}
> +		return NMI_HANDLED;
> +	}
> +	return NMI_DONE;
> +}


SNIP