Hi,
I looked into the IOAT code today as I'm trying to find out how to add support
for it to NFS. I ran into this piece of code, which waits for the DMA
operation to complete:
while (dma_async_memcpy_complete(tp->ucopy.dma_chan,
tp->ucopy.dma_cookie, &done,
&used) == DMA_IN_PROGRESS) {
/* do partial cleanup of sk_async_wait_queue */
while ((skb = skb_peek(&sk->sk_async_wait_queue)) &&
(dma_async_is_complete(skb->dma_cookie, done,
used) == DMA_SUCCESS)) {
__skb_dequeue(&sk->sk_async_wait_queue);
kfree_skb(skb);
}
}
Nowhere in the dma_async_*complete functions can I see any code
that would sleep if the DMA is not yet complete. Am I missing something,
or are we really busy-waiting on the DMA engine? Wouldn't this kind of
defeat the purpose of freeing up the CPU from the chores of memcpying?
I also checked the code in ioatdma.c - I would have expected there to
be some kind of interrupt handler that kicks the upper layers when a
DMA operation completes. But the interrupt handler seems to be for
error reporting exclusively...
Olaf
--
Olaf Kirch | --- o --- Nous sommes du soleil we love when we play
[EMAIL PROTECTED] | / | \ sol.dhoop.naytheet.ah kin.ir.samse.qurax
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