linux-kernel - Re: [PATCH V2 3/3] x86, bm: Add documentation on Intel Branch Monitoring

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Date:   Tue, 12 Dec 2017 13:05:04 -0800
From:   Megha Dey <megha.dey@...el.com>
To:     Jiri Olsa <jolsa@...hat.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
Subject: Re: [PATCH V2 3/3] x86, bm: Add documentation on Intel Branch
 Monitoring

On Mon, 2017-11-20 at 15:07 +0100, Jiri Olsa wrote:
> On Fri, Nov 17, 2017 at 05:54:06PM -0800, Megha Dey wrote:
> 
> SNIP
> 
> > +IV. User-configurable inputs
> > +============================
> > +
> > +Several sysfs entries are provided in /sys/devices/intel_bm/ to configure
> > +controls for the supported hardware heuristics.
> > +
> > +1. LBR freeze: /sys/devices/intel-bm/lbr_freeze
> > +   possible values are 0 or 1. By default this is disabled(0). When enabled,
> > +   an LBR freeze is observed on threshold trip
> > +
> > +2. Guest Disable: /sys/devices/intel-bm/guest_disable
> > +   Possible values are 0 or 1. By default it is 0. When set to ‘1’, branch
> > +   monitoring feature is disabled when operating at VMX non-root operation.
> > +
> > +3. Window size: /sys/devices/intel-bm/window_size
> > +   By default, window size is 1023. It can take values from 0 to 1023. This
> > +   represents the number of instructions to be executed before the event
> > +   counters are reset.
> > +
> > +4. Window count select: /sys/devices/intel-bm/window_cnt_sel
> > +   Possible values are:
> > +   ‘00 = instructions retired
> > +   ‘01 = branches retired
> > +   ‘10 = returned instructions retired
> > +   ‘11 = indirect branch instructions retired
> > +   By default, it has a value of 0.
> > +
> > +5. Count and mode: /sys/devices/intel-bm/cnt_and_mode
> > +   Possible values are 0 or 1. By default it is 0. When set to ‘1’, the
> > +   overall event triggering condition is true only if both enabled
> > +   counter’s threshold conditions are true. When ‘0’, the threshold
> > +   tripping condition is true if either enabled counter’s threshold is
> > +   true. If a counter is not enabled, then it does not factor into the
> > +   AND’ing logic
> > +
> > +6. Threshold: /sys/devices/intel-bm/threshold
> > +   An unsigned value of 0 to 127 is supported. The value 0 of counter
> > +   threshold will result in branch monitoring event signaled after every
> > +   instruction. By default, it has a value of 127.
> > +
> > +7. Mispredict counting behaviour: /sys/devices/intel-bm/mispred_evt_cnt
> > +   Possible values are:
> > +   0 = mispredict events are counted in a window
> > +   1 = mispredict events are counted based on a consecutive occurrence.
> > +   By default, it has a value of 0.
> 
> you use all those value to configure the event:
> 
>         event->hw.bm_ctrl = (bm_window_size << BM_WINDOW_SIZE_SHIFT) |
>                             (bm_guest_disable << BM_GUEST_DISABLE_SHIFT) |
>                             (bm_lbr_freeze << BM_LBR_FREEZE_SHIFT) |
>                             (bm_window_cnt_sel << BM_WINDOW_CNT_SEL_SHIFT) |
>                             (bm_cnt_and_mode << BM_CNT_AND_MODE_SHIFT) |
>                                                                 BM_ENABLE;
>         event->hw.bm_counter_conf = (bm_threshold << BM_THRESHOLD_SHIFT) |
>                         (bm_mispred_evt_cnt << BM_MISPRED_EVT_CNT_SHIFT) |
>                         (cfg << BM_EVENT_TYPE_SHIFT) | BM_CNTR_ENABLE;
> 
> I wonder you should place this under perf_event_attr::config/config1
> and define them in /sys/devices/intel_bm/format/... like we do for
> cpu pmu
> 
> then you could use perf stat -e like: '-e intel_bm/call-ret,threshold=...,lbr_freeze/'

Thanks for the suggestion! I will implement this in the next patch set.
> 
> jirka