linux-kernel - Re: [RFC PATCH 0/3] latencytop lock usage improvement

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Message-ID: <20190430091033.GN2623@hirez.programming.kicks-ass.net>
Date:   Tue, 30 Apr 2019 11:10:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...nel.org>,
        Eric W Biederman <ebiederm@...ssion.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ying Huang <ying.huang@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] latencytop lock usage improvement

On Tue, Apr 30, 2019 at 04:35:05PM +0800, Feng Tang wrote:
> Hi Peter,
> 
> On Tue, Apr 30, 2019 at 10:09:10AM +0200, Peter Zijlstra wrote:
> > On Mon, Apr 29, 2019 at 04:03:28PM +0800, Feng Tang wrote:
> > > Hi All,
> > > 
> > > latencytop is a very nice tool for tracing system latency hotspots, and
> > > we heavily use it in our LKP test suites.
> > 
> > What data does latency-top give that perf cannot give you? Ideally we'd
> > remove latencytop entirely.
> 
> Thanks for the review. In 0day/LKP test service, we have many tools for
> monitoring and analyzing the test results, perf is the most important
> one, which has the most parts in our auto-generated comparing results.   
> For example to identify spinlock contentions and system hotspots.
> 
> latencytop is another tool we used to find why systems go idle, like why
> workload chose to sleep or waiting for something. 

You're not answering the question; why can't you use perf for that? ISTR
we explicitly added support for things like that.