linux-kernel - Re: [RFC 00/13] perf: Add perf kwork

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Message-ID: <YrR34345A4h/5RfU@li-be644d4c-2c59-11b2-a85c-bc3dba3ed00b.ibm.com>
Date:   Thu, 23 Jun 2022 09:25:39 -0500
From:   "Paul A. Clarke" <pc@...ibm.com>
To:     Yang Jihong <yangjihong1@...wei.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, namhyung@...nel.org,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [RFC 00/13] perf: Add perf kwork

On Thu, Jun 23, 2022 at 09:02:45AM +0800, Yang Jihong wrote:
> On 2022/6/22 22:59, Paul A. Clarke wrote:
> > On Mon, Jun 13, 2022 at 05:45:52PM +0800, Yang Jihong wrote:
> > > Sometimes, we need to analyze time properties of kernel work such as irq,
> > > softirq, and workqueue, such as delay and running time of specific interrupts.
> > > Currently, these events have kernel tracepoints, but perf tool does not
> > > directly analyze the delay of these events
> > > 
> > > The perf-kwork tool is used to trace time properties of kernel work
> > > (such as irq, softirq, and workqueue), including runtime, latency,
> > > and timehist, using the infrastructure in the perf tools to allow
> > > tracing extra targets
> > > 
> > > test case:
> > > 
> > >    # perf kwork report
> > > 
> > >      Kwork Name                | Cpu  | Total Runtime | Frequency | Max runtime   | Max runtime start   | Max runtime end     |
> > >     ---------------------------------------------------------------------------------------------------------------------------
> > >      (s)RCU:9                  | 0007 |      3.488 ms |      1258 |      0.145 ms |    3398384.220013 s |    3398384.220157 s |
> > >      (s)NET_RX:3               | 0003 |      1.866 ms |       156 |      0.042 ms |    3398385.629764 s |    3398385.629806 s |
> > >      (s)TIMER:1                | 0000 |      1.799 ms |       117 |      0.055 ms |    3398385.568033 s |    3398385.568088 s |
> > >      (w)0xffff9c66e563ee98     | 0006 |      1.561 ms |         5 |      0.351 ms |    3398384.060021 s |    3398384.060371 s |
> > 
> > What units are used for "Frequency"? It would be helpful to include somewhere.

> This refers to the number of event in the trace period.

I see. I suggest changing the column heading to say that.
"Count", "Number of Events", "Occurrences", something like that.

"Frequency" is a count-per-time-unit, like hertz, which doesn't
match well here.

PC