Quoting r. Stephen Hemminger <[EMAIL PROTECTED]>: > Subject: Re: Dropping NETIF_F_SG since no checksum feature. > > O > > > > > > You might want to try ignoring the check in dev.c and testing > > > to see if there is a performance gain. It wouldn't be hard to test > > > a modified version and validate the performance change. > > > > Yes. With my patch, there is a huge performance gain by increasing MTU to > > 64K. > > And it seems the only way to do this is by S/G. > > > > > You could even do what I suggested and use skb_checksum_help() > > > to do inplace checksumming, as a performance test. > > > > I can. But as network algorithmics says (chapter 5) > > "Since such bus reads are expensive, the CPU might as well piggyback > > the checksum computation with the copy process". > > > > It speaks about onboard the adapter buffers, but memory bus reads are also > > much slower > > than CPU nowdays. So I think even if this works well in benchmark in real > > life > > single copy should better. > > > > The other alternative might be to make copy/checksum code smarter about using > fragments rather than allocating a large buffer. It should avoid second order > allocations (effective size > PAGESIZE). In my testing, it seems quite smart already - once I declare F_SG and clear F_...CSUM I start getting properly checksummed packets with lots of s/g fragments. But I'm not catching the drift - an alternative to what this would be?
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