From: Herbert Xu <[EMAIL PROTECTED]> Date: Thu, 31 Aug 2006 23:18:33 +1000
> The Xen performance problem turned out to be something else altogether. > It was an incorrect rcv mss estimate which leads to delayed acks. So > it's not a bug in Linux yet :) However, since we need this for LRO as > well, here's a patch for net-2.6.19. Good spotting. > [TCP]: Fix rcv mss estimate for LRO > > By passing a Linux-generated TSO packet straight back into Linux, Xen > becomes our first LRO user :) Unfortunately, there is at least one spot > in our stack that needs to be changed to cope with this. > > The receive MSS estimate is computed from the raw packet size. This is > broken if the packet is GSO/LRO. Fortunately the real MSS can be found > in gso_size so we simply need to use that if it is non-zero. > > Real LRO NICs should of course set the gso_size field in future. > > Signed-off-by: Herbert Xu <[EMAIL PROTECTED]> Ok, I'll put this into net-2.6.19, but I think it deserves serious consideration for 2.6.18 because the S2IO driver does implement HW LRO and it is almost certainly getting bitten by this issue since I do not see that driver setting gso_size, and perhaps the current S2io firmware implementing this cannot provide the MSS value needed. - 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
