Compact Flash PIO 4 tuning

Compact Flash PIO 4 tuning

[David Wuertele]

Howdy,

I'm working on an embedded system that has a CF card on the IDE bus.
The CF spec only allows PIO mode, and my card can do PIO 4.  However,
when I try to stream data from this card into memory at 2 MBytes per
second, it pegs the CPU at 100%.  This is ruining the performance of
my application, which has to process this data in real time.

I realize that PIO 4 requires CPU involvement, but are there ways I
can tune the kernel for copying large files to memory, so that my
application doesn't get starved of CPU?

Thanks,
Dave

Re: Compact Flash PIO 4 tuning

[Vojtech Pavlik]

On Mon, May 05, 2003 at 05:53:35PM -0700, David Wuertele wrote:
> Howdy,
> 
> I'm working on an embedded system that has a CF card on the IDE bus.
> The CF spec only allows PIO mode, and my card can do PIO 4.  However,
> when I try to stream data from this card into memory at 2 MBytes per
> second, it pegs the CPU at 100%.  This is ruining the performance of
> my application, which has to process this data in real time.
> 
> I realize that PIO 4 requires CPU involvement, but are there ways I
> can tune the kernel for copying large files to memory, so that my
> application doesn't get starved of CPU?

If you use the full bandwidth of the PIO device, you use 100% CPU.
That's it and there's no way around. You can check that the IDE/CF
interface is set to PIO4 and that under Linux you have IRQ unmasking
enabled, those two will help, though the first statement is still
valid.

-- 
Vojtech Pavlik
SuSE Labs, SuSE CR