> On Thursday 17 November 2011 00:15:42 Michael Büsch wrote:
> > On Thu, 17 Nov 2011 00:12:03 +0100
> > Christian Lamparter <chunkeey@xxxxxxxxxxxxxx> wrote:
> > > BTW: I always wondered if it would make sense to have a
> > > cached rx skb ready in p54spi_rx(). This way we don't
> > > have to do DMA onto the stack [which is really ugly and
> > > possibly illegal] and might even get a better rx
> > > performance. I could write the code but as you know I don't
> > > have the hardware to test it.
> >
> > I'll test it, if you can come up with a patch.
> ---
> [RFC] p54spi: don't DMA onto the stack
>
> DMA transfers should not be done onto the kernel stack.
What about p54spi_read32, it does the same thing?
I have tested this patch, it works, no measurable rx speed boost though
(~6.1Mbit/sec in iperf as either server or client).
[...snip...]
> - if (len <= READAHEAD_SZ) {
> - memcpy(skb_put(skb, len), rx_head + 1, len);
> + if (len <= READAHEAD) {
> + skb_put(skb, len);
> } else {
> - memcpy(skb_put(skb, READAHEAD_SZ), rx_head + 1, READAHEAD_SZ);
> + skb_put(skb, READAHEAD);
> p54spi_spi_read(priv, SPI_ADRS_DMA_DATA,
> - skb_put(skb, len - READAHEAD_SZ),
> - len - READAHEAD_SZ);
> + skb_put(skb, len - READAHEAD),
> + len - READAHEAD);
> }
I have also tested this patch without this (READAHEAD_SZ) kludge.
It appears to work now.
Thanks.
-- Max
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