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    SubjectRe: PATCH: Fix broken PIO with libata
    On 5/16/06, Tejun Heo <htejun@gmail.com> wrote:
    > Jeff Garzik wrote:
    > > Kevin Radloff wrote:
    > >> On 5/16/06, Alan Cox <alan@lxorguk.ukuu.org.uk> 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@gmail.com
    http://thesaq.com/
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