netdev - Re: stmmac ethernet in kernel 4.4: coalescing related pauses?

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Message-ID: <20161130102857.GA14296@amd>
Date:   Wed, 30 Nov 2016 11:28:57 +0100
From:   Pavel Machek <pavel@....cz>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>, lsanfil@...vell.com,
        peppe.cavallaro@...com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: stmmac ethernet in kernel 4.4: coalescing related pauses?

On Mon 2016-11-28 07:31:43, Eric Dumazet wrote:
> On Mon, 2016-11-28 at 09:54 -0500, David Miller wrote:
> > From: Lino Sanfilippo <lsanfil@...vell.com>
> > Date: Mon, 28 Nov 2016 14:07:51 +0100
> > 
> > > Calling skb_orphan() in the xmit handler made this issue disappear.
> > 
> > This is not the way to handle this problem.
> > 
> > The solution is to free the SKBs in a timely manner after the
> > chip has transmitted the frame.
> 
> Note that the 'pauses' described by Pavel are also caused by a too small
> SO_SNDBUF value on the UDP socket.
> 
> An immediate fix, with no kernel change is to increase it.
> 
> echo 1000000 >/proc/sys/net/core/wmem_default

Thanks a lot. For the record, that works around the problem, too. (Or
at least helps a lot; it may be possible that problem still remains if
continuous stream of packets is going to trigger this, if I read the
sources correctly.)

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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