Messages in this thread | | | Date | Mon, 19 Jul 2004 13:34:31 +0200 | From | Ingo Molnar <> | Subject | Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch |
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* Ingo Molnar <mingo@elte.hu> wrote:
> 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.
typically all of this happens with irqs enabled (unmask=1), but it still increases scheduling latencies.
with the default DMA setup of today's ATA hw there can be a maximum of 256 entries in the sg-table all zapped in ide_end_request() -> __end_that_request_first().
Plus the IDE driver also builds the sg-table of the next request in hardirq context. (ide_build_dmatable() and ide_build_sglist()).
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