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Date:   Wed, 10 Apr 2019 16:44:18 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Aaron Lu <aaron.lu@linux.alibaba.com>
Cc:     Tim Chen <tim.c.chen@linux.intel.com>, mingo@kernel.org,
        tglx@linutronix.de, pjt@google.com, torvalds@linux-foundation.org,
        linux-kernel@vger.kernel.org, subhra.mazumdar@oracle.com,
        fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com,
        Aubrey Li <aubrey.intel@gmail.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>
Subject: Re: [RFC][PATCH 13/16] sched: Add core wide task selection and
 scheduling.
Message-ID: <20190410144418.GH2490@worktop.programming.kicks-ass.net>
References: <20190218165620.383905466@infradead.org>
 <20190218173514.667598558@infradead.org>
 <20190402064612.GA46500@aaronlu>
 <20190402082812.GJ12232@hirez.programming.kicks-ass.net>
 <20190405145530.GA453@aaronlu>
 <460ce6fb-6a40-4a72-47e8-cf9c7c409bef@linux.intel.com>
 <20190410043633.GA67532@aaronlu>
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On Wed, Apr 10, 2019 at 12:36:33PM +0800, Aaron Lu wrote:
> On Tue, Apr 09, 2019 at 11:09:45AM -0700, Tim Chen wrote:
> > Now that we have accumulated quite a number of different fixes to your orginal
> > posted patches.  Would you like to post a v2 of the core scheduler with the fixes?
> 
> One more question I'm not sure: should a task with cookie=0, i.e. tasks
> that are untagged, be allowed to scheduled on the the same core with
> another tagged task?

That was not meant to be possible.

> The current patch seems to disagree on this, e.g. in pick_task(),
> if max is already chosen but max->core_cookie == 0, then we didn't care
> about cookie and simply use class_pick for the other cpu. This means we
> could schedule two tasks with different cookies(one is zero and the
> other can be tagged).

When core_cookie==0 we shouldn't schedule the other siblings at all.

> But then sched_core_find() only allow idle task to match with any tagged
> tasks(we didn't place untagged tasks to the core tree of course :-).
> 
> Thoughts? Do I understand this correctly? If so, I think we probably
> want to make this clear before v2. I personally feel, we shouldn't allow
> untagged tasks(like kernel threads) to match with tagged tasks.

Agreed, cookie should always match or idle.