Date:   Thu, 9 Mar 2023 13:44:13 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Mike Galbraith <efault@gmx.de>
Cc:     mingo@kernel.org, vincent.guittot@linaro.org,
        linux-kernel@vger.kernel.org, juri.lelli@redhat.com,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, corbet@lwn.net,
        qyousef@layalina.io, chris.hyser@oracle.com,
        patrick.bellasi@matbug.net, pjt@google.com, pavel@ucw.cz,
        qperret@google.com, tim.c.chen@linux.intel.com, joshdon@google.com,
        timj@gnu.org, kprateek.nayak@amd.com, yu.c.chen@intel.com,
        youssefesmat@chromium.org, joel@joelfernandes.org
Subject: Re: [PATCH 10/10] sched/fair: Implement an EEVDF like policy
Message-ID: <ZAnUnSEJ92bKpim7@hirez.programming.kicks-ass.net>
References: <20230306132521.968182689@infradead.org>
 <20230306141502.810909205@infradead.org>
 <bfbfbf041854e2cd1a8ed14e64081062e5d632d3.camel@gmx.de>
 <9fd2c37a05713c206dcbd5866f67ce779f315e9e.camel@gmx.de>
 <20230309090633.GK2017917@hirez.programming.kicks-ass.net>
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On Thu, Mar 09, 2023 at 10:06:33AM +0100, Peter Zijlstra wrote:
> Hi Mike!
> 
> On Wed, Mar 08, 2023 at 02:36:01PM +0100, Mike Galbraith wrote:
> > On Wed, 2023-03-08 at 09:39 +0100, Mike Galbraith wrote:
> > >
> > > Curiosity got the best of me...
> > 
> > Remember this little bugger, allegedly distilled from a real
> > application control thread starvation issue?
> 
> Oooh, yeah, I should still have that somewhere. I'll try and remember
> what exactly was needed to make it behave properly.

That thing wants both wakeup preemption and sleeper bonus. Specifically,
it needs the signal to insta-preempt the 'pointless' kill loop.

What happens is that while positive lag, we get this, when negative lag
happens wakeup-preemption is not achieved and we get delayed by a full
tick.

This gets us very little actual runtime.

Let me see what do do about that...