Message-ID: <4206E01E.6060408@kolivas.org>
Date: Mon, 07 Feb 2005 14:27:26 +1100
From: Con Kolivas <kernel@kolivas.org>
User-Agent: Mozilla Thunderbird 1.0 (X11/20041206)
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To: "Jack O'Quin" <joq@io.com>
Cc: Werner Almesberger <wa@almesberger.net>,
       linux <linux-kernel@vger.kernel.org>,
       abiss-general@lists.sourceforge.net
Subject: Re: [PATCH]sched: Isochronous class v2 for unprivileged soft rt scheduling
References: <41EEE1B1.9080909@kolivas.org> <41EF00ED.4070908@kolivas.org>	<873bwwga0w.fsf@sulphur.joq.us> <41EF123D.703@kolivas.org>	<87ekgges2o.fsf@sulphur.joq.us> <41EF2E7E.8070604@kolivas.org>	<87oefkd7ew.fsf@sulphur.joq.us> <41EF48BA.50709@kolivas.org>	<20050207000922.B25338@almesberger.net> <87acqhnj6h.fsf@sulphur.joq.us>
In-Reply-To: <87acqhnj6h.fsf@sulphur.joq.us>
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Jack O'Quin wrote:
> Werner Almesberger <wa@almesberger.net> writes:
> 
> 
>>[ Cc:s trimmed, added abiss-general ]
>>
>>Con Kolivas wrote:
>>
>>>Possibly reiserfs journal related. That has larger non-preemptible code 
>>>sections.
>>
>>If I understand your workload right, it should consist mainly of
>>computation, networking (?), and disk reads.
> 
> 
> The jack_test3.2 is basically a multiprocess realtime audio test.  A
> fair amount of computation, signifcant task switch overhead, but
> most I/O is to the sound card.
> 
> There's some disk activity starting clients and probably some other
> system activity in the background.
> 
> 
>>I don't know much about ReiserFS, but in some experiments with ext3,
>>using ABISS, we found that a reader application competing with best
>>effort readers would experience worst-case delays of dozens of
>>milliseconds.
>>
>>They were caused by journaled atime updates. Mounting the file
>>system with "noatime" reduced delays to a few hundred microseconds
>>(still worst-case).
> 
> 
> Interesting. Worth a try to verify.  Con was seeing a 6msec delay
> every 20 seconds.  This was devastating to the test, which tries to
> run a full realtime audio cycle every 1.45msec.

They already were mounted noatime :(

Con

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