Messages in this thread | | | Date | Mon, 22 Nov 2004 15:42:48 +0100 | From | Ingo Molnar <> | Subject | Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.30-2 |
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* Eran Mann <emann@mrv.com> wrote:
> >>I´m seeing latencies of up to ~2000 microseconds. see attached traces > >>file for a small sample. I think I´m missing something obvious > >>config-wise but I don´t know what... > ... > > >this seems to imply IDE DMA related hardware overhead. Apparently what > >happens is that with certain motherboards/chipsets, if IDE DMA happens > >then that DMA transfer _completely locks up_ the system bus. Nothing > >happens, and the CPU is stalled in essence until the end of the DMA > >request.
> Right on. > After hdparm -d0 I see maximum latency of 35 us after a full kernel > build with a few GUI apps in the background. I´ll try to find a > reasonable compromise.
it might make sense to report this to the hw vendor as well, as these latencies dont occur at _every_ IDE DMA, it might be some sort of chipset (or BIOS) bug they might want to see resolved as well (if this isnt a ship-and-forget vendor). 2 msec stalls are not nice to a fair number of applications.
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