netdev - Re: [net-next 1/1] tipc: reduce risk of wakeup queue starvation

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Message-Id: <20190801.181959.616930719935387626.davem@davemloft.net>
Date:   Thu, 01 Aug 2019 18:19:59 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     jon.maloy@...csson.com
Cc:     netdev@...r.kernel.org, gordan.mihaljevic@...tech.com.au,
        tung.q.nguyen@...tech.com.au, hoang.h.le@...tech.com.au,
        canh.d.luu@...tech.com.au, ying.xue@...driver.com,
        tipc-discussion@...ts.sourceforge.net
Subject: Re: [net-next 1/1] tipc: reduce risk of wakeup queue starvation

From: Jon Maloy <jon.maloy@...csson.com>
Date: Tue, 30 Jul 2019 16:23:18 +0200

> In commit 365ad353c256 ("tipc: reduce risk of user starvation during
> link congestion") we allowed senders to add exactly one list of extra
> buffers to the link backlog queues during link congestion (aka
> "oversubscription"). However, the criteria for when to stop adding
> wakeup messages to the input queue when the overload abates is
> inaccurate, and may cause starvation problems during very high load.
> 
> Currently, we stop adding wakeup messages after 10 total failed attempts
> where we find that there is no space left in the backlog queue for a
> certain importance level. The counter for this is accumulated across all
> levels, which may lead the algorithm to leave the loop prematurely,
> although there may still be plenty of space available at some levels.
> The result is sometimes that messages near the wakeup queue tail are not
> added to the input queue as they should be.
> 
> We now introduce a more exact algorithm, where we keep adding wakeup
> messages to a level as long as the backlog queue has free slots for
> the corresponding level, and stop at the moment there are no more such
> slots or when there are no more wakeup messages to dequeue.
> 
> Fixes: 365ad35 ("tipc: reduce risk of user starvation during link congestion")
> Reported-by: Tung Nguyen <tung.q.nguyen@...tech.com.au>
> Acked-by: Ying Xue <ying.xue@...driver.com>
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>

Applied, thank you.