linux-kernel - Re: [RFC PATCH 2/3] perf tools: Add support for "report" for some spe events

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Date:   Wed, 16 Oct 2019 10:12:43 +0000
From:   James Clark <James.Clark@....com>
To:     Tan Xiaojun <tanxiaojun@...wei.com>,
        Jeremy Linton <Jeremy.Linton@....com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
        "yao.jin@...ux.intel.com" <yao.jin@...ux.intel.com>,
        "tmricht@...ux.ibm.com" <tmricht@...ux.ibm.com>,
        "brueckner@...ux.ibm.com" <brueckner@...ux.ibm.com>,
        "songliubraving@...com" <songliubraving@...com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Kim Phillips <Kim.Phillips@....com>
CC:     "gengdongjiu@...wei.com" <gengdongjiu@...wei.com>,
        "wxf.wang@...ilicon.com" <wxf.wang@...ilicon.com>,
        "liwei391@...wei.com" <liwei391@...wei.com>,
        "huawei.libin@...wei.com" <huawei.libin@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        Al Grant <Al.Grant@....com>, nd <nd@....com>
Subject: Re: [RFC PATCH 2/3] perf tools: Add support for "report" for some spe
 events

Hi Xiaojun,

>>
>> What do you mean when the user specifies "event:pp", if the SPE is available, configure and record the spe data directly via the perf event open syscall?
>> (perf.data itself is the same as using -e arm_spe_0//xxx?)
> 
> I mean, for the perf record, if the user does not add ":pp" to these events, the original process is taken, and if ":pp" is added, the spe process is taken.
> 

Yes we think this is the best way to do it considering that SPE has been implemented as a separate PMU and it will be very difficult to do it in the Kernel when the precise_ip attribute is set.

I think doing everything in userspace is easiest. This will at least mean that users of Perf don't have to be aware of the details of SPE to get precise sample data.

So if the user specifies "event:p" when SPE is available, the SPE PMU is automatically configured data is recorded. If the user also specifies -e arm_spe_0//xxx and wants to do some manual configuration, then that could override the automatic configuration.


James