Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.30-2

[Ingo Molnar]

* Eran Mann <emann@xxxxxxx> 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.

	Ingo
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