linux-kernel - Re: [RFD/RFC PATCH 0/8] Towards implementing proxy execution

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Date:   Wed, 10 Oct 2018 15:48:56 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Henrik Austad <henrik@...tad.us>
Cc:     Juri Lelli <juri.lelli@...hat.com>, mingo@...hat.com,
        rostedt@...dmis.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        alessio.balsini@...il.com, will.deacon@....com,
        andrea.parri@...rulasolutions.com, dietmar.eggemann@....com,
        patrick.bellasi@....com, linux-rt-users@...r.kernel.org
Subject: Re: [RFD/RFC PATCH 0/8] Towards implementing proxy execution

On 10/10/18 2:24 PM, Peter Zijlstra wrote:
>> I believe there were some papers circulated last year that looked at 
>> something similar to this when you had overlapping or completely disjoint 
>> CPUsets I think it would be nice to drag into the discussion. Has this been 
>> considered? (if so, sorry for adding line-noise!)
> Hurm, was that one of Bjorn's papers? Didn't that deal with AC of
> disjoint/overlapping sets?
> 

This paper:
https://people.mpi-sws.org/~bbb/papers/pdf/rtsj14.pdf

But, unless I am wrong, there were findings after this paper that shows
some imprecision on it.

Anyway, it does not analyse the locking properties, only scheduler of
independent tasks - it is a start, but far from what we do here.

(btw this paper is really complex...)

The locking problem for such case: APA with the nesting of different
locks in the locking implementation (we use raw spin lock on this, and
this method could also be used in the rw lock/sem in the future, nesting
rw_lock(mutex_proxy(raw_spinlock())) is an open problem from the
academic point of view.

I explained these things (nested lock and the need of APA for locking)
as "Open Problems" at the RTSOPs (part of the ECRTS) earlier this year:

http://rtsops2018.loria.fr/wp-content/uploads/2018/07/RTSOPS18_proceedings_final.pdf

Bjorn were there, but not only him... Baruah, Davis, Alan Burns were there.

There are some works being done for more complex locking in academy, like:

https://www.cs.unc.edu/~jarretc/papers/ecrts18b_long.pdf

But still, the task model used on these implementations are not the
Linux one.

-- Daniel