netdev - Re: [PATCH net] tcp/dccp: do not block bh too long in inet_twdr_twkill

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Message-ID: <1428679861.25985.311.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 10 Apr 2015 08:31:01 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] tcp/dccp: do not block bh too long in
 inet_twdr_twkill_work()

On Fri, 2015-04-10 at 04:19 -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> I have seen inet_twdr_twkill_work() blocking softirq for
> periods up to 1.5 seconds, depending on number of timewait sockets.
> 
> This is an unacceptable source of latency.
> 
> Note that inet_twdr_do_twkill_work() releases death_lock spinlock
> for every tw handled, but does not take care of bh enabling.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---

BTW, inet_twdr_twcal_tick() suffers from similar problem, with latencies
of ~25ms, when /proc/sys/net/ipv4/tcp_tw_recycle is enabled.

Since it holds death_lock for the whole run, all other cpus are spinning
on it.

I believe we simply should add a timer per timewait, as I did for
request sockets.

This would simplify the code a lot, and would get rid of this awful non
scalable timer wheel.


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