linux-kernel - Re: [PATCH 0/7] introduce cpu.headroom knob to cpu controller

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Message-ID: <20190521134730.GA12346@blackbody.suse.cz>
Date:   Tue, 21 May 2019 15:47:30 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Song Liu <songliubraving@...com>
Cc:     Morten Rasmussen <morten.rasmussen@....com>,
        Kernel Team <Kernel-team@...com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] introduce cpu.headroom knob to cpu controller

Hello Song.

On Wed, Apr 10, 2019 at 07:43:35PM +0000, Song Liu <songliubraving@...com> wrote:
> The load level above is measured as requests-per-second. 
> 
> When there is no side workload, the system has about 45% busy CPU with 
> load level of 1.0; and about 75% busy CPU at load level of 1.5. 
> 
> The saturation starts before the system hitting 100% utilization. This is
> true for many different resources: ALUs in SMT systems, cache lines, 
> memory bandwidths, etc. 
I have read through the thread continuation and it appears to me there
is some misunderstanding on the latency metric (scheduler latency <=
your latency <= request wall time?).

Could you please describe how is the latency that you report defined and
measured?

Thanks,
Michal


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