From:	Benno Senoner <sbenno@gardena.net>
To:	linux-kernel@vger.kernel.org,
Subject: Ingo's lowlatency-test7-A0 excellent latencies (<1msec), but kernel filesync problems ...
Date:	Wed, 13 Sep 2000 00:09:18 +0200

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)

see the graph here:
http://www.linuxdj.com/latency/2.4.0-test7-lowlatency-A0/2048.html

(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)

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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