Subject: Re: [linux-audio-dev] Ingo's lowlatency-test7-A0 excellent latencies (<1msec), but kernel filesync problems ...
From: Chris Baugher (baugher_AT_enteract.com)
Date: Wed Sep 13 2000 - 00:29:44 EEST
On Wed, 13 Sep 2000, Benno Senoner wrote:
> Hi folks,
> I benchmarked Ingo's lowlatency-2.4.0-test7-A0 kernel
> (http://people.redhat.com/mingo/lowlatency-patches/lowlatency-2.4.0-test7-A0)
>
> I can only say that it looks VERY promising ( < 1msec latencies !)
> But there seems to be problems with the kernel disk sync code:
> After the disk stress test, I call the "sync" command, but unfortunately
> the sync process hangs and eats 100% of the CPU (but no kernel crash)
I also had similar problems with with not being able to complete the tests
because of the sync call hanging. The tests that did finish looked really
good though!
>
> see the graph here:
> http://www.linuxdj.com/latency/2.4.0-test7-lowlatency-A0/2048.html
Looks alot like the graphs I got.
> (disk copy and disk read tests are missing because, of the hanging sync)
>
> Is this perhaps related to the truncate bug fixed in -test8 ?
>
> Ingo, any ideas what the cause of the hang could be ?
> (let us know please when you port the patch to test8)
Yes, definitely!
Chris|
>
> Anyway if the remaining bugs can be fixed, then I think that that
> all low latency needs of 2.4 users will be satisfied.
> (my reference mark is being able to stay below 1.5 - 2msec, which
> is needed for perceptually delayfree realtime audio processing)
>
> PS: looking at the results Chris posted,
> http://cygnus.ipal.org/results-2.4.0t8-ll/3x256.html
> Andrew's minimalistic approach looks promising too and seems to
> be able to guarantee <5msec latencies under high load.
>
> cheers,
> Benno.
>
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