Re: net: more accurate skb truesize - regression on Microblaze

[Eric Dumazet <eric.dumazet@gmail.com>]

On Tue, 2012-04-10 at 11:29 +0200, Michal Simek wrote:
> On 04/10/2012 11:24 AM, Eric Dumazet wrote:
> > On Tue, 2012-04-10 at 11:11 +0200, Michal Simek wrote:
> >
> >> ~ # cat /proc/sys/net/ipv4/tcp_rmem
> >> 4096    87380   130048
> >
> > Are they default values, or tuned by admin ?
> >
> > 130048 bytes isnt enough to let TCP open its rcv window.
> 
> yep. Default value after powerup. What's wrong with that?
> 
> Michal
> 

I guess your tcp performance is driven by these numbers mostly.

receive window wont grow above 64K in these case. a tcpdump could
confirm the issue.

Do you have 130000 pages of memory ?

Seems the net/ipv4/tcp.c code is wrong (or the comment is wrong)

Since its not 1/128 but 1/1024 ....


        /* Set per-socket limits to no more than 1/128 the pressure threshold */
        limit = nr_free_buffer_pages() << (PAGE_SHIFT - 10);
        limit = max(limit, 128UL);
        max_share = min(4UL*1024*1024, limit);

        sysctl_tcp_wmem[0] = SK_MEM_QUANTUM;
        sysctl_tcp_wmem[1] = 16*1024;
        sysctl_tcp_wmem[2] = max(64*1024, max_share);

        sysctl_tcp_rmem[0] = SK_MEM_QUANTUM;
        sysctl_tcp_rmem[1] = 87380;
        sysctl_tcp_rmem[2] = max(87380, max_share);