Re: USB and FireWire performance (again)
Re: USB and FireWire performance (again)
- Subject: Re: USB and FireWire performance (again)
- From: Jeff Moore <email@hidden>
- Date: Wed, 26 Feb 2003 18:02:32 -0800
The HAL has a hard limit of roughly 90% CPU usage as measured against
the deadlines it calculates internally before it will put you in the
penalty box and issue kAudioDevicePropertyOverload notifications (this
will forcibly drop at least buffer's worth of data too), so even with
DMA'd hardware, you can't really push the CPU that hard without
glitching. Top is terrible at getting an accurate reading of the load
in the IO thread, so you have to do more extreme profiling to get a
true judge of how much CPU you are using.
Both USB and FireWire have to do work on lower priority kernel threads
in order to function properly. Doing lots of work in time constraint
threads will hose the hardware. This is one of the reasons why Bill
says not to use this kind of thread for feeder threads. You set up more
conditions where you can inadvertently hose the hardware. Also, some
devices are more susceptible to these problems then others are.
On Thursday, February 27, 2003, at 02:45 PM, Lubor Prikryl wrote:
Hi,
(Thanks to Jeff and others for their help).
I am more than satisfied with CoreAudio ability to run Audio I/O with
very high priority. Using PCI audio cards, there are no clicks up to
98% CPU load (menus and windows open several minutes in this case).
But there is a serious problem with USB and (I was surprised)
FireWire. When the CPU is loaded to more than 70%, there are dropouts
and clicks. It must be something with higher priority than
USB/FireWire, but lower than audio, blocking I/O. What is this? Is
there a possibility to give this thread greater priority? It seems to
be a general I/O thread, isn't it?
Thanks
Lubor, DSound
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--
Jeff Moore
Core Audio
Apple
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