Re: PATCH: Fix broken PIO with libata

[Kevin Radloff]

On 5/16/06, Tejun Heo <htejun@xxxxxxxxx> wrote:
> Jeff Garzik wrote:
> > Kevin Radloff wrote:
> >> On 5/16/06, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
> >>> On Maw, 2006-05-16 at 11:33 -0400, Kevin Radloff wrote:
> >>> > However, I still have a problem with pata_pcmcia (that I actually
> >>> > experienced also with the ide-cs driver) where sustained reading or
> >>> > writing to the CF card spikes the CPU with nearly 100% system time.
> >>>
> >>> That is normal. The PCMCIA devices don't support DMA. As a result of
> >>> this the processor has to fetch each byte itself over the ISA speed
> >>> PCMCIA bus link.
> >>
> >> Hrm, as I recall that only started happening with ide-cs sometime in
> >> the single digits of 2.6.x.. And note that it's only maxing out at
> >> about 1.5MB/s. Should that saturate my laptop's 1.1GHz Pentium M
> >> processor?
> >
> > Doing data xfer using PIO rather than DMA definitely eats tons of CPU
> > cycles.
>
> Yeap, in addition, if doing real PIO (unbuffered by the HBA), the time
> it takes is soley determined by what PIO mode is in use.  It doesn't
> matter how fast the CPU is.  Faster CPUs only end up wasting more
> cycles.  :-(

(oops, hit 'reply', but given the incredible importance of my response... ;P)

Ah, well then never mind. ;) I just have a dim memory of it being
different a long time ago. At least it works now. :D

--
Kevin 'radsaq' Radloff
radsaq@xxxxxxxxx
http://thesaq.com/
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