netdev - Re: [PATCH net-next] tcp/dccp: get rid of central timewait timer

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Date:	Sun, 12 Apr 2015 18:41:13 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tcp/dccp: get rid of central timewait timer

On Sun, 2015-04-12 at 21:33 -0400, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Fri, 10 Apr 2015 12:19:34 -0700
> 
> > From: Eric Dumazet <edumazet@...gle.com>
> > 
> > Using a timer wheel for timewait sockets was nice ~15 years ago when
> > memory was expensive and machines had a single processor.
> > 
> > This does not scale, code is ugly and source of huge latencies
> > (Typically 30 ms have been seen, cpus spinning on death_lock spinlock.)
> > 
> > We can afford to use an extra 64 bytes per timewait sock and spread
> > timewait load to all cpus to have better behavior.
> > 
> > Tested:
>  ...
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> 
> First of all, I had to munge your commit message by hand.  All of
> those ping output lines that start with '---' tell 'git am' "commit
> message ends here" so most of your test results got removed.  I added
> them back by hand.
> 
> Second of all, this doesn't compile:
> 
> net/ipv4/tcp_minisocks.c: In function ‘tcp_time_wait’:
> net/ipv4/tcp_minisocks.c:283:27: warning: passing argument 2 of ‘inet_twsk_alloc’ from incompatible pointer type
>   tw = inet_twsk_alloc(sk, &tcp_death_row.tw_count, state);
>                            ^
> In file included from include/linux/tcp.h:24:0,
>                  from include/net/tcp.h:24,
>                  from net/ipv4/tcp_minisocks.c:26:
> include/net/inet_timewait_sock.h:108:28: note: expected ‘struct inet_timewait_death_row *’ but argument is of type ‘struct atomic_t *’
>  struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,

Arf, I am sorry, I missed this warning, and resulting kernel was correct
as tw_count was the first field of this structure.

Will send a v2.




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