linux-kernel - Re: [PATCH v7 3/3] KVM: perf: kvm events analysis tool

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Date:	Thu, 13 Sep 2012 08:14:37 -0600
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	Dong Hao <haodong@...ux.vnet.ibm.com>,
	xiaoguangrong@...ux.vnet.ibm.com, avi@...hat.com,
	mtosatti@...hat.com, Ingo Molnar <mingo@...nel.org>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v7 3/3] KVM: perf: kvm events analysis tool

On 9/13/12 7:45 AM, Arnaldo Carvalho de Melo wrote:
> Em Wed, Sep 12, 2012 at 10:56:44PM -0600, David Ahern escreveu:
>>>>   static const char * const kvm_usage[] = {
>>>> +    "perf kvm [<options>] {top|record|report|diff|buildid-list|stat}",
>
>>> The usage for the report/record sub commands of stat is never shown. e.g.,
>>> $ perf kvm stat
>>> --> shows help for perf-stat
>
>>> $ perf kvm
>>> --> shows the above and perf-kvm's usage
>>
>> [I deleted this thread, so having to reply to one of my responses.
>> hopefully noone is unduly harmed by this.]
>>
>> I've been using this command a bit lately -- especially on nested
>> virtualization -- and I think the syntax is quirky - meaning wrong.
>> In my case I always follow up a record with a report and end up
>> using a shell script wrapper that combines the 2 and running it
>> repeatedly. e.g.,
>>
>>      $PERF kvm stat record -o $FILE -p $pid -- sleep $time
>>      [ $? -eq 0 ] && $PERF --no-pager kvm  -i $FILE stat report
>>
>> As my daughter likes to say - awkward.
>>
>> That suggests what is really needed is a 'live' mode - a continual
>> updating of the output like perf top, not a record and analyze later
>> mode. Which does come back to why I responded to this email -- the
>> syntax is klunky and awkward.
>>
>> So, I spent a fair amount of time today implementing a live mode.
>> And after a lot of swearing at the tracepoint processing code I
>
> What kind of swearing? I'm working on 'perf test' entries for
> tracepoints to make sure we don't regress on the perf/libtraceevent
> junction, doing that as prep work for further simplifying tracepoint
> tools like sched, kvm, kmem, etc.

Have you seen how the tracing initialization is done? ugly. record 
generates tracing data events and report uses those to do the init so 
you can access the raw_data. I ended up writing this:

static int perf_kvm__tracing_init(void)
{
     struct tracing_data *tdata;
     char temp_file[] = "/tmp/perf-XXXXXXXX";
     int fd;

     fd = mkstemp(temp_file);
     if (fd < 0) {
         pr_err("mkstemp failed\n");
         return -1;
     }
     unlink(temp_file);

     tdata = tracing_data_get(&kvm_events.evlist->entries, fd, false);
     if (!tdata)
         return -1;
     lseek(fd, 0, SEEK_SET);
     (void) trace_report(fd, &kvm_events.session->pevent, false);
     tracing_data_put(tdata);

     return 0;
}


>
>> finally have it working. And the format extends easily (meaning <
>> day and the next step) to a perf-based kvm_stat replacement. Example
>> syntax is:
>>
>>     perf kvm stat [-p <pid>|-a|...]
>>
>> which defaults to an update delay of 1 second, and vmexit analysis.
>>
>> The guts of the processing logic come from the existing kvm-events
>> code. The changes focus on combining the record and report paths
>> into one. The display needs some help (Arnaldo?), but it seems to
>> work well.
>>
>> I'd like to get opinions on what next? IMO, the record/report path
>> should not get a foot hold from a backward compatibility perspective
>> and having to maintain those options. I am willing to take the
>> existing patches into git to maintain authorship and from there
>> apply patches to make the live mode work - which includes a bit of
>> refactoring of perf code (like the stats changes).
>>
>> Before I march down this path, any objections, opinions, etc?
>
> Can I see the code?

Let me clean it up over the weekend and send out an RFC for it.

David
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