Re: [PATCH] fix limited slow start bug

Ilpo Järvinen wrote:

BTW, while looking this patch, I noticed that snd_cwnd_clamp is only u16 
while snd_cwnd is u32, which seems rather strange since snd_cwnd is being 
limited by the clamp value here and there?!?! And tcp_highspeed.c is 
clearly assuming even more than this (but the problem is hidden as 
snd_cwnd_clamp is feed back to the min_t and the used 32-bit constant 
could be safely cut to 16-bits anyway):

  tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);

Has the type being changed somewhere in the past or why is this so?

It's been that way as long as I can remember.  It's always been a 
mystery to me as well.  I suspect the tcp_highspeed code is that way 
because this patch originally came out of the Web100-patched kernel, 
which at one point was using a 32 bit snd_cwnd_clamp IIRC.

I think it's not unreasonable to change clamp to 32 bits now, since with 
1500 byte packets, this corresponds to a max cwnd of ~94MB.  This is 
pretty big, but we are currently right at this limit with 10 GigE.

   -John