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SubjectRe: [PATCH v2] perf/x86/intel: Add support for MISPREDICT bit on Knights Landing cpus
<div dir="ltr">I do not understand the difference between linear address vs effective address but LBR_FORMAT_EIP_FLAGS implies effective address, no?<div><div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jul 31, 2018 at 12:17 AM, Peter Zijlstra <span dir="ltr">&lt;<a href="mailto:peterz@infradead.org" target="_blank">peterz@infradead.org</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5">On Mon, Jul 30, 2018 at 10:28:13PM +0800, Jacek Tomaka wrote:<br>
&gt; From: Jacek Tomaka &lt;<a href="mailto:jacek.tomaka@poczta.fm">jacek.tomaka@poczta.fm</a>&gt;<br>
&gt; <br>
&gt; Problem: perf did not show branch predicted/mispredicted bit in brstack.<br>
&gt; <br>
&gt; Output of perf -F brstack for profile collected<br>
&gt; <br>
&gt; Before: <br>
&gt; 0x4fdbcd/0x4fdc03/-/-/-/0<br>
&gt; 0x45f4c1/0x4fdba0/-/-/-/0<br>
&gt; 0x45f544/0x45f4bb/-/-/-/0<br>
&gt; 0x45f555/0x45f53c/-/-/-/0<br>
&gt; 0x7f66901cc24b/0x45f555/-/-/-/<wbr>0<br>
&gt; 0x7f66901cc22e/0x7f66901cc23d/<wbr>-/-/-/0<br>
&gt; 0x7f66901cc1ff/0x7f66901cc20f/<wbr>-/-/-/0<br>
&gt; 0x7f66901cc1e8/0x7f66901cc1fc/<wbr>-/-/-/0<br>
&gt; <br>
&gt; After: <br>
&gt; 0x4fdbcd/0x4fdc03/P/-/-/0<br>
&gt; 0x45f4c1/0x4fdba0/P/-/-/0<br>
&gt; 0x45f544/0x45f4bb/P/-/-/0<br>
&gt; 0x45f555/0x45f53c/P/-/-/0<br>
&gt; 0x7f66901cc24b/0x45f555/P/-/-/<wbr>0<br>
&gt; 0x7f66901cc22e/0x7f66901cc23d/<wbr>P/-/-/0 <br>
&gt; 0x7f66901cc1ff/0x7f66901cc20f/<wbr>P/-/-/0<br>
&gt; 0x7f66901cc1e8/0x7f66901cc1fc/<wbr>P/-/-/0<br>
&gt; <br>
&gt; Cause: <br>
&gt; As mentioned in Software Development Manual vol 3, 17.4.8.1,<br>
&gt; IA32_PERF_CAPABILITIES[5:0] indicates the format of the address that is<br>
&gt; stored in the LBR stack. Knights Landing reports 1 (LBR_FORMAT_LIP) as<br>
&gt; its format. Despite that, registers containing FROM address of the branch,<br>
&gt; do have MISPREDICT bit but because of the format indicated in<br>
&gt; IA32_PERF_CAPABILITIES[5:0], LBR did not read MISPREDICT bit.<br>
&gt; <br>
&gt; Solution: <br>
&gt; Teach LBR about above Knights Landing quirk and make it read MISPREDICT bit.<br>
&gt; ---<br>
&gt;  arch/x86/events/intel/lbr.c | 6 +++++-<br>
&gt;  1 file changed, 5 insertions(+), 1 deletion(-)<br>
&gt; <br>
&gt; diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c<br>
&gt; index cf372b9055..043aa09f3a 100644<br>
&gt; --- a/arch/x86/events/intel/lbr.c<br>
&gt; +++ b/arch/x86/events/intel/lbr.c<br>
&gt; @@ -19,7 +19,7 @@ enum {<br>
&gt;       LBR_FORMAT_MAX_KNOWN    = LBR_FORMAT_TIME,<br>
&gt;  };<br>
&gt;  <br>
&gt; -static const enum {<br>
&gt; +static enum {<br>
&gt;       LBR_EIP_FLAGS           = 1,<br>
&gt;       LBR_TSX                 = 2,<br>
&gt;  } lbr_desc[LBR_FORMAT_MAX_KNOWN + 1] = {<br>
&gt; @@ -1230,4 +1230,8 @@ void intel_pmu_lbr_init_knl(void)<br>
&gt;  <br>
&gt;       x86_pmu.lbr_sel_mask = LBR_SEL_MASK;<br>
&gt;       x86_pmu.lbr_sel_map  = snb_lbr_sel_map;<br>
&gt; +<br>
&gt; +     /* Knights Landing does have MISPREDICT bit */<br>
&gt; +     if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_LIP)<br>
&gt; +             lbr_desc[LBR_FORMAT_LIP] |= LBR_EIP_FLAGS;<br>
&gt;  }<br>
<br>
</div></div>So why not set lbr_format to LBR_FORMAT_EIP_FLAGS ?<br>
</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><span><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><font color="#000000"><font face="arial,helvetica,sans-serif"><b>Jacek Tomaka</b></font></font><br><font color="#000000"><font face="arial,helvetica,sans-serif"><font size="2">Geophysical Software Developer</font></font></font><br></div><font color="#000000" face="arial,helvetica,sans-serif">
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