Messages in this thread | | | Date | Tue, 20 Jul 2004 09:11:36 +0200 | From | Ingo Molnar <> | Subject | Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch |
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* Lee Revell <rlrevell@joe-job.com> wrote:
> But the current behavior only causes latency problems for an IDE > system, so if this were made runtime-tunable then it would only be an > issue for SATA, right? This would cover 99.9% of audio users, who > would gladly trade some disk throughput for lower latency. You can > record a *lot* of tracks with even a few MB/s of disk throughput.
it's an issue for all block IO drivers that do IO completions from IRQ context and that can do DMA - i.e. every block IO hardware that uses interrupts. This includes SCSI too. In fact for SCSI it's a norm to have tagged queueing active so there the latencies ought to be even higher (although i havent measured this). IDE/PATA's limitation in this regard limits latencies as well.
being able to control the max size of sg-tables and the max # of outstanding commands per IRQ source [this later should already be possible via driver options] should enable us to control the maximum hardirq latency introduced by block IO.
(if the hardware & disk is fast enough, or you use a high # of controllers and disks then you could still overload your system with a stream of interrupts and cause unbound scheduling latencies - but this is a separate problem.)
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