linux-kernel - Re: [PATCH 0/2] Notifications for perf sideband events

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Date:   Thu, 13 Jul 2017 19:50:02 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Jiri Olsa <jolsa@...hat.com>,
        Vince Weaver <vincent.weaver@...ne.edu>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Notifications for perf sideband events


[ Adding Vince...]


On 2017/07/12 12:48PM, Jiri Olsa wrote:
> On Mon, Jun 19, 2017 at 08:01:06PM +0530, Naveen N. Rao wrote:
> > Currently, there is no way to ask for signals to be delivered when a
> > certain number of sideband events have been logged into the ring buffer.
> > This is problematic if we are only interested in, say, context switch
> > events. Furthermore, signals are more useful (rather than polling) for
> > self-profiling. This series provides for a way to achieve this.
> > 
> > We ride on top of the existing support for ring buffer wakeup to
> > generate signals as desired. Counting sideband events still requires
> > some changes in the output path, but in normal cases, it ends up being
> > just a comparison.
> > 
> > The test program below demonstrates how a process can profile itself for
> > context switch events and how it can control notification through
> > signals. The key changes include the below perf_event_attr settings as
> > well as use of IOC_ENABLE:
> > 	pe.signal_on_wakeup = 1;
> > 	pe.count_sb_events = 1;
> > 	pe.wakeup_events = 2;
> 
> Vince,
> could you please check on this? thanks
> 
> Naveen,
> have you run Vince's test suite on this?
>   http://github.com/deater/perf_event_tests.git

I just tried this and I see quite a few failures even without these 
patches.

The behavior is similar with/without these patches and all the ioctl 
tests pass, but I see some failures with the overflow tests. I'll look 
into those tests in detail tomorrow. I may be missing something.


Thanks,
Naveen