Messages in this thread | | | Date | Tue, 3 Feb 2009 13:25:35 +0100 | From | Willy Tarreau <> | Subject | Re: [PATCH v2] tcp: splice as many packets as possible at once |
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On Tue, Feb 03, 2009 at 03:18:36PM +0300, Evgeniy Polyakov wrote: > On Tue, Feb 03, 2009 at 11:12:09PM +1100, Herbert Xu (herbert@gondor.apana.org.au) wrote: > > The only change we need to make is at receive time. Instead of > > always pushing the received skb into the stack, we should try to > > allocate a linear replacement skb, and if that fails, allocate > > a fragmented skb and copy the data into it. That way we can > > always push a linear skb back into the ring buffer. > > Yes, that's was the part about 'reserve' buffer for the sockets you cut > :) > > I agree that this will work and will be better than nothing, but copying > 9kb into 3 pages is rather CPU hungry operation, and I think (but have > no numbers though) that system will behave faster if MTU is reduced to > the standard one.
Well, FWIW, I've always observed better performance with 4k MTU (4080 to be precise) than with 9K, and I think that the overhead of allocating 3 contiguous pages is a major reason for this.
> Another solution is to have a proper allocator which will be able to > defragment the data, if talking about the alternatives to the drop. > > So: > 1. copy the whole jumbo skb into fragmented one > 2. reduce the MTU
you'll not reduce MTU of established connections though. And trying to advertise MSS changes in the middle of a TCP connection is an awful hack which I think will not work everywhere.
> 3. rely on the allocator > > For the 'good' hardware and drivers nothing from the above is really needed. > > -- > Evgeniy Polyakov
Willy
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