netdev - Re: [PATCH v2] sctp: avoid refreshing heartbeat timer too often

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Message-Id: <20160410.222332.1053521794879934365.davem@davemloft.net>
Date:	Sun, 10 Apr 2016 22:23:32 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	marcelo.leitner@...il.com
Cc:	netdev@...r.kernel.org, nhorman@...driver.com, vyasevich@...il.com,
	David.Laight@...LAB.COM, linux-sctp@...r.kernel.org
Subject: Re: [PATCH v2] sctp: avoid refreshing heartbeat timer too often

From: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Date: Wed,  6 Apr 2016 15:15:19 -0300

> Currently on high rate SCTP streams the heartbeat timer refresh can
> consume quite a lot of resources as timer updates are costly and it
> contains a random factor, which a) is also costly and b) invalidates
> mod_timer() optimization for not editing a timer to the same value.
> It may even cause the timer to be slightly advanced, for no good reason.
> 
> As suggested by David Laight this patch now removes this timer update
> from hot path by leaving the timer on and re-evaluating upon its
> expiration if the heartbeat is still needed or not, similarly to what is
> done for TCP. If it's not needed anymore the timer is re-scheduled to
> the new timeout, considering the time already elapsed.
> 
> For this, we now record the last tx timestamp per transport, updated in
> the same spots as hb timer was restarted on tx. Also split up
> sctp_transport_reset_timers into sctp_transport_reset_t3_rtx and
> sctp_transport_reset_hb_timer, so we can re-arm T3 without re-arming the
> heartbeat one.
> 
> On loopback with MTU of 65535 and data chunks with 1636, so that we
> have a considerable amount of chunks without stressing system calls,
> netperf -t SCTP_STREAM -l 30, perf looked like this before:
 . ..
> And after this patch, now with netperf -l 60:
 ...
> Throughput-wise, from 6800mbps without the patch to 7050mbps with it,
> ~3.7%.
> 
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>

Applied, thanks Marcelo.