To: Ingo Molnar <mingo@elte.hu>
Cc: Chris Wright <chrisw@osdl.org>, Matt Mackall <mpm@selenic.com>,
       Paul Davis <paul@linuxaudiosystems.com>,
       Christoph Hellwig <hch@infradead.org>, Andrew Morton <akpm@osdl.org>,
       Lee Revell <rlrevell@joe-job.com>, arjanv@redhat.com,
       alan@lxorguk.ukuu.org.uk, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] [request for inclusion] Realtime LSM
References: <20050110212019.GG2995@waste.org>
	<200501111305.j0BD58U2000483@localhost.localdomain>
	<20050111191701.GT2940@waste.org>
	<20050111125008.K10567@build.pdx.osdl.net>
	<20050111205809.GB21308@elte.hu>
	<20050111131400.L10567@build.pdx.osdl.net>
	<20050111212719.GA23477@elte.hu> <87fz15j325.fsf@sulphur.joq.us>
	<20050115134922.GA10114@elte.hu> <874qhiwb1q.fsf@sulphur.joq.us>
From: "Jack O'Quin" <joq@io.com>
Date: Sat, 15 Jan 2005 17:38:11 -0600
In-Reply-To: <874qhiwb1q.fsf@sulphur.joq.us> (Jack O'Quin's message of "Sat,
 15 Jan 2005 17:02:41 -0600")
Message-ID: <871xcmuuu4.fsf@sulphur.joq.us>
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>> * Jack O'Quin <joq@io.com> wrote:
>>> One major problem: this `nice --20' hack affects every thread, not
>>> just the critical realtime ones.  That's not what we want.  Audio
>>> applications make very conscious choices which threads run with high
>>> priority and which do not.

> Ingo Molnar <mingo@elte.hu> writes:
>> how much did this problem affect your test? Could the source of the 500
>> msec delays be the non-highprio components of the test that somehow
>> became nice --20?

Jack O'Quin <joq@io.com> writes:
> Probably, the best way to tell would be patching JACK so it uses
> nice(-20) instead of pthread_setschedparam() for the realtime threads.
> As a hack, that looks easy.  I'll build a working directory with just
> that change, so we can experiment with it better.

Bah!  Nothing is ever as easy as it looks.

According to the manpage, nice(2) is per-process not per-thread.  That
does not give the granularity we need.  

Is that correct?  If so, I can't think of any way to make this work.
Suggestions?

We need to allow both realtime and non-realtime threads in the same
process.  Anything less would require an enormous rewrite for most
audio programs, an unreasonable thing to ask.
-- 
  joq
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