Re: [linux-audio-dev] interesting 2.3.4* kernel statistic

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Subject: Re: [linux-audio-dev] interesting 2.3.4* kernel statistic
From: David Olofson (david_AT_gardena.net)
Date: ti helmi  22 2000 - 20:25:21 EST


On Tue, 22 Feb 2000, Benno Senoner wrote:
> I am a little confused by the numbers:
> With the lowlatency patches we achieve <2-3ms latencies ALWAYS,
> even when closing files etc.
> Latencytest ran on my P133 while accessing the disk heavily , stress proc ,
> and copying the entrire content of two CDs from TWO CDROM drives
> simultaneously, and a close() call is issued zillions of time during my tests.

This was on a "standard" 2.3.4x kernel, as I understand it (after
actually reading the posts this time ;-) - not a lowlatency patched
kernel.

> Therefore I don't understand how/if the lockmetering can be applied to do any
> inferency on how small latencies we can get out of our realtime apps.

A lock only stalls threads that hit them while they're locked by
other threads... That is, you might avoid getting that big latencies
because your RT thread never forces the kernel to grab those locks.
For example, do you need the do_close lock to just access an open
device? The idea with all these locks in the newer kernels is to
avoid having a global lock (or even worse, simply disable IRQs on all
CPUs) while touching the sensitive structs.

//David

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