linux-kernel - Re: [RFC 4/8] Improve the tracking of active utilisation

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Message-ID: <20160128140053.GR6356@twins.programming.kicks-ass.net>
Date:	Thu, 28 Jan 2016 15:00:53 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	luca abeni <luca.abeni@...tn.it>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@....com>
Subject: Re: [RFC 4/8] Improve the tracking of active utilisation

On Thu, Jan 28, 2016 at 02:41:29PM +0100, luca abeni wrote:

> > Some day we should fix this :-)

> I am trying to have a better look at the code, and I think that
> implementing bandwidth inheritance (BWI) could be easy (implementing
> M-BWI, that can be analyzed on multi-processor systems, is more complex
> because it requires busy waiting or similar).

Ah indeed, I remember now. To which I said that if busy-waiting is
'correct' so then must not busy-waiting be, for that consumes less
cputime and would allow more actual work to be done.

Of course, I might have missed some subtle detail, but intuition
suggests the above.

> > Nope, but fixing this is likely to be non-trivial.

> Ok... So, if this is acceptable for this patchset I'll try to keep the
> current PI behaviour,

Yeah that's fine. That's decidedly outside the scope of these patches.

> and I'll try to have a look at a better PI
> protocol after the runtime reclaiming stuff is done (that is, I make it
> acceptable for mainline, or we decide that a different approach is
> needed).

That would be very nice indeed!