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Message-ID: <1121439115.42d7cd8b3f372@vds.kolivas.org>
Date: Sat, 16 Jul 2005 00:51:55 +1000
From: kernel@kolivas.org
To: Lee Revell <rlrevell@joe-job.com>
Cc: Zwane Mwaikambo <zwane@arm.linux.org.uk>,
       Linus Torvalds <torvalds@osdl.org>, Vojtech Pavlik <vojtech@suse.cz>,
       Arjan van de Ven <arjan@infradead.org>,
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       Chris Wedgwood <cw@f00f.org>, Andrew Morton <akpm@osdl.org>,
       "Brown, Len" <len.brown@intel.com>, dtor_core@ameritech.net,
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       linux-kernel@vger.kernel.org, mbligh@mbligh.org, diegocg@gmail.com,
       azarah@nosferatu.za.org, christoph@lameter.com
Subject: Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt
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Quoting Lee Revell <rlrevell@joe-job.com>:

> On Thu, 2005-07-14 at 22:54 -0600, Zwane Mwaikambo wrote:
> > On Fri, 15 Jul 2005, Lee Revell wrote:
> > 
> > > On Fri, 2005-07-15 at 14:08 +1000, Con Kolivas wrote:
> > > > Audio did show slightly larger max latencies but nothing that would be
> of 
> > > > significance.
> > > > 
> > > > On video, maximum latencies are only slightly larger at HZ 250, all the
> 
> > > > desired cpu was achieved, but the average latency and number of missed
> 
> > > > deadlines was significantly higher.
> > > 
> > > Because audio timing is driven by the soundcard interrupt while video,
> > > like MIDI, relies heavily on timers.
> > 
> > In interbench it's not driven by a soundcard interrupt.
> > 
> > 
> 
> OK.  Con, any idea why video is so much more affected than audio?

In the emulation, video vs audio is 40% cpu vs 5% cpu, 16.7ms frames instead of
50ms frames. When your cpu requirements are higher and your frames are shorter
the likelihood of dropping a frame, especially under load, will skyrocket as
your timing granularity decreases. Clearly 250HZ is not as good as 1000HZ for
this, and I assume your midi example.

Cheers,
Con