From: Jeff Garzik <[EMAIL PROTECTED]>
Date: Fri, 02 Mar 2007 22:14:39 -0500
> Chris Leech wrote:
> > Every 20 descriptors turns out to be to few append commands with
> > newer/faster CPUs. Pushing every 4 still cuts down on MMIO writes to an
> > acceptable level without letting the DMA engine run out of work.
> >
> > Signed-off-by: Chris Leech <[EMAIL PROTECTED]>
> > ---
> >
> > drivers/dma/ioatdma.c | 4 ++--
> > 1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/dma/ioatdma.c b/drivers/dma/ioatdma.c
> > index 8e87261..0f77a9d 100644
> > --- a/drivers/dma/ioatdma.c
> > +++ b/drivers/dma/ioatdma.c
> > @@ -310,7 +310,7 @@ static dma_cookie_t do_ioat_dma_memcpy(struct
> > ioat_dma_chan *ioat_chan,
> > list_splice_init(&new_chain, ioat_chan->used_desc.prev);
> >
> > ioat_chan->pending += desc_count;
> > - if (ioat_chan->pending >= 20) {
> > + if (ioat_chan->pending >= 4) {
>
> This sounds like something that will always be wrong -- or in other
> words, always be right for only the latest CPUs. Can this be made
> dynamic, based on some timing factor?
In fact I think this has been tweaked twice in the vanilla tree
already.
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