netdev - Re: [PATCH net-next] tcp: improve latencies of timer triggered events

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Message-Id: <20120720.110128.205223157733612873.davem@davemloft.net>
Date:	Fri, 20 Jul 2012 11:01:28 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, therbert@...gle.com, ycheng@...gle.com,
	ncardwell@...gle.com, nanditad@...gle.com, johnwheffner@...il.com,
	hkchu@...gle.com
Subject: Re: [PATCH net-next] tcp: improve latencies of timer triggered
 events

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 20 Jul 2012 17:45:50 +0200

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Modern TCP stack highly depends on tcp_write_timer() having a small
> latency, but current implementation doesn't exactly meet the
> expectations.
> 
> When a timer fires but finds the socket is owned by the user, it rearms
> itself for an additional delay hoping next run will be more
> successful.
> 
> tcp_write_timer() for example uses a 50ms delay for next try, and it
> defeats many attempts to get predictable TCP behavior in term of
> latencies.
> 
> Use the recently introduced tcp_release_cb(), so that the user owning
> the socket will call various handlers right before socket release.
> 
> This will permit us to post a followup patch to address the
> tcp_tso_should_defer() syndrome (some deferred packets have to wait
> RTO timer to be transmitted, while cwnd should allow us to send them
> sooner)
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

I like this a lot, applied, thanks Eric.
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