Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

[Ingo Molnar]

* Lee Revell <rlrevell@xxxxxxxxxxx> wrote:

> Just as a reference point, what do you think is the longest delay I
> *should* be seeing?  I recall hearing that BEOS guaranteed that
> interrupts are never disabled for more than 50 usecs.  This seems
> achievable, as the average delay I am seeing is 15 usecs.

ATA hardirq latency can be as high as 700 usecs under load even on
modern hw, when big DMA requests are created with long scatter-gather
lists. We also moved some of the page IO completion code into irq
context which further increased hardirq latencies. Since these all touch
cold cachelines it all adds up quite quickly.

	Ingo
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