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Date:   Fri, 23 Oct 2020 13:59:45 -0400
From:   Joel Fernandes <joel@joelfernandes.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
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        Tim Chen <tim.c.chen@intel.com>
Subject: Re: [PATCH v8 -tip 06/26] sched: Add core wide task selection and
 scheduling.
Message-ID: <20201023175945.GB3563800@google.com>
References: <20201020014336.2076526-1-joel@joelfernandes.org>
 <20201020014336.2076526-7-joel@joelfernandes.org>
 <20201023150544.GG2974@worktop.programming.kicks-ass.net>
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On Fri, Oct 23, 2020 at 05:05:44PM +0200, Peter Zijlstra wrote:
> On Mon, Oct 19, 2020 at 09:43:16PM -0400, Joel Fernandes (Google) wrote:
> > From: Peter Zijlstra <peterz@infradead.org>
> > 
> > Instead of only selecting a local task, select a task for all SMT
> > siblings for every reschedule on the core (irrespective which logical
> > CPU does the reschedule).
> 
> This:
> 
> > 
> > During a CPU hotplug event, schedule would be called with the hotplugged
> > CPU not in the cpumask. So use for_each_cpu(_wrap)_or to include the
> > current cpu in the task pick loop.
> > 
> > There are multiple loops in pick_next_task that iterate over CPUs in
> > smt_mask. During a hotplug event, sibling could be removed from the
> > smt_mask while pick_next_task is running. So we cannot trust the mask
> > across the different loops. This can confuse the logic. Add a retry logic
> > if smt_mask changes between the loops.
> 
> isn't entirely accurate anymore, is it?

Yes you are right, we need to delete this bit from the changelog. :-(. I'll
go do that.

thanks,

 - Joel