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Date: Tue, 19 Jul 2011 13:56:25 -0700 From: Shirley Ma <mashirle@...ibm.com> To: "Michael S. Tsirkin" <mst@...hat.com> Cc: David Miller <davem@...emloft.net>, netdev@...r.kernel.org, jasowang@...hat.com Subject: Re: [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers On Tue, 2011-07-19 at 22:09 +0300, Michael S. Tsirkin wrote: > On Tue, Jul 19, 2011 at 11:37:58AM -0700, Shirley Ma wrote: > > Signed-off-by: Shirley Ma <xma@...ibm.com> > > --- > > > > drivers/vhost/net.c | 6 ++++-- > > 1 files changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > index 70ac604..83cb738 100644 > > --- a/drivers/vhost/net.c > > +++ b/drivers/vhost/net.c > > @@ -189,8 +189,10 @@ static void handle_tx(struct vhost_net *net) > > break; > > } > > /* If more outstanding DMAs, queue the work */ > > - if (unlikely(vq->upend_idx - vq->done_idx > > > - VHOST_MAX_PEND)) { > > + if (unlikely((vq->upend_idx - vq->done_idx > > > + VHOST_MAX_PEND) || > > + (vq->upend_idx - vq->done_idx > > > + VHOST_MAX_PEND - > UIO_MAXIOV))) { > > Could you please explain why this makes sense please? > VHOST_MAX_PEND is 128 UIO_MAXIOV is 1024 so > the result is negative? I thought it is equal to: if (vq->upend_idx > vq->done_idx) check vq->upend_idx - vq->done_idx > VHOST_MAX_PEND if (vq->upend_idx < vq->done_idx) check vq->upend_idx + UIO_MAXIOV - vq->done_idx > VHOST_MAX_PEND > I thought upend_idx - done_idx is exactly the number > of buffers, so once we get too many we stop until > one gets freed? They are index, so in vhost zerocopy callback, we can get the idx right away. > > > tx_poll_start(net, sock); > > set_bit(SOCK_ASYNC_NOSPACE, > &sock->flags); > > break; > > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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