On Tue, 7 Mar 2006 00:34:38 +0200 "Michael S. Tsirkin" <[EMAIL PROTECTED]> wrote:
> Hello, Dave! > As you might know, the TSO patches merged into mainline kernel > since 2.6.11 have hurt performance for the simple (non-TSO) > high-speed netdevice that is IPoIB driver. > > This was discussed at length here > http://openib.org/pipermail/openib-general/2005-October/012271.html > > I'm trying to figure out what can be done to improve the situation. > In partucular, I'm looking at the Super TSO patch > http://oss.sgi.com/archives/netdev/2005-05/msg00889.html > > merged into mainline here > > http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=314324121f9b94b2ca657a494cf2b9cb0e4a28cc > > There, you said: > > When we do ucopy receive (ie. copying directly to userspace > during tcp input processing) we attempt to delay the ACK > until cleanup_rbuf() is invoked. Most of the time this > technique works very well, and we emit one ACK advertising > the largest window. > > But this explodes if the ucopy prequeue is large enough. > When the receiver is cpu limited and TSO frames are large, > the receiver is inundated with ucopy processing, such that > the ACK comes out very late. Often, this is so late that > by the time the sender gets the ACK the window has emptied > too much to be kept full by the sender. > > The existing TSO code mostly avoided this by keeping the > TSO packets no larger than 1/8 of the available window. > But with the new code we can get much larger TSO frames. > > So I'm trying to get a handle on it: could a solution be to simply > look at the frame size, and call tcp_send_delayed_ack from > if the frame size is no larger than 1/8? > > Does this make sense? > > Thanks, > > More likely you are getting hit by the fact that TSO prevents the congestion window from increasing properly. This was fixed in 2.6.15 (around mid of Nov 2005). - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
