Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Sender: Tejun Heo <htejun@gmail.com>
Date:   Tue, 22 Mar 2022 06:40:46 -1000
From:   Tejun Heo <tj@kernel.org>
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, linux-kernel@vger.kernel.org, parth@linux.ibm.com,
        qais.yousef@arm.com, chris.hyser@oracle.com,
        pkondeti@codeaurora.org, Valentin.Schneider@arm.com,
        patrick.bellasi@matbug.net, David.Laight@aculab.com,
        pjt@google.com, pavel@ucw.cz, dhaval.giani@oracle.com,
        qperret@google.com, tim.c.chen@linux.intel.com
Subject: Re: [RFC 6/6] sched/fair: Add sched group latency support
Message-ID: <Yjn8DohJ8CZ6pEvf@slm.duckdns.org>
References: <20220311161406.23497-1-vincent.guittot@linaro.org>
 <20220311161406.23497-7-vincent.guittot@linaro.org>
 <Yji0twS4N+0b/Rs9@slm.duckdns.org>
 <CAKfTPtA8g-MJMPRM2R_Bfo9rGSyR3cYAUy_j5UrRM+SAB=Mm7w@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAKfTPtA8g-MJMPRM2R_Bfo9rGSyR3cYAUy_j5UrRM+SAB=Mm7w@mail.gmail.com>
Precedence: bulk

Hello,

On Tue, Mar 22, 2022 at 05:10:36PM +0100, Vincent Guittot wrote:
> latency_nice is quite similar to nice. The nice latency is used as an
> index to get a latency weight in the range [-1024:1024].  latency_nice
> is in the range [-20:19] and latency_prio shifts it in the range
> [0:40] . This index is then used to get the latency weight similar to
> how the nice prio is used to get a weight. That being said, the
> latency should probably reflect the latency_weight instead of the
> latency_prio in order to be aligned with the weight and weight.nice
> fields of cgroups.
> 
> As described in patch 5 commit message, the weight is then used to
> compute a relative offset to check whether the waking task can preempt
> the current running task.

So, what I'm trying to say is if it is actually a weight, just use weight
values instead of arbitrary mapped nice values. Nobody can tell how the
latency nice value of -2 compares against, say, 3. If you can define it
clearly in terms of weights (or something else clearly describable), it'd be
a lot better.

Thanks.

-- 
tejun