Re: scheduling question
Re: scheduling question
- Subject: Re: scheduling question
- From: rimas avizienis <email@hidden>
- Date: Thu, 15 Jan 2004 22:19:40 -0800 (PST)
i have written a low latency coreaudio driver which
sends and receives UDP packets containing audio out
over the network interface to a special purpose piece
of hardware i've built. In order to get the
performance/latency/etc i needed when the machine was
running under a heavy load (doing real time processing
of live audio, etc) I had to modify the
AppleGMACEthernet.kext driver so that the main loop
in my coreaudio driver (get packet, copy buffers, call
taketimestamp, send a packet out) gets called at
primary interrupt time (highest priority in the
system) by using checkForInterrupt instead of just
interruptOccurred and having it call my coreaudio
driver. I basically bypassed the whole networking
stack.
You might need to do something of that sort...
-rimas
--- Mike Smith <email@hidden> wrote:
>
On Jan 15, 2004, at 1:31 AM, Stefan Werner wrote:
>
>
> Are there other tweaks to enhance the latency of
>
networking? I don't
>
> mind a decrease in throughput, I'm in one of the
>
rare cases where
>
> bandwidth is not the limit. There are these
>
popular "bandwidth tuner"
>
> tweaks where people change the system's TCP buffer
>
size with sysctls,
>
> would shrinking the buffers give me any latency
>
improvements or will
>
> that result in dropped packets?
>
>
It won't help; the system already tries to give you
>
the lowest possible
>
latency. There's not really any more blood to
>
squeeze from the stone.
>
>
It's important, back in the design stage, to take
>
into consideration
>
that you're going to be running in a multiprogrammed
>
environment and
>
try to take this into account there, rather than
>
trying to tweak a
>
system that can't give you guarantees to fit a
>
design that assumes a
>
particular value of "reasonable".
>
>
Obviously this isn't always possible.
>
>
= Mike
>
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