netdev - Re: 3.19+: (and quite probably earlier) VIA Rhine hanging under high network load, yet again: redux

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Message-ID: <20150405231510.GA15719@electric-eye.fr.zoreil.com>
Date:	Mon, 6 Apr 2015 01:15:10 +0200
From:	Francois Romieu <romieu@...zoreil.com>
To:	Nix <nix@...eri.org.uk>
Cc:	rl@...lgate.ch, Bjarke Istrup Pedersen <gurligebis@...too.org>,
	"David S. Miller" <davem@...emloft.net>,
	Linux-Netdev <netdev@...r.kernel.org>
Subject: Re: 3.19+: (and quite probably earlier) VIA Rhine hanging under high
 network load, yet again: redux

Nix <nix@...eri.org.uk> :
[...]
> Gross or not, it seems to work: I've loaded it enough to crash it half a
> dozen times, and not a crash. However, the rx_dropped stats on the link
> aren't going up, so maybe I've just been lucky.

Rx descriptors are now recycled as soon as they are processed whereas the
driver used to perform a complete processing batch before recycling any
descriptor. It could make a huge difference.

The pre-patch rx batch recycling did not include any barrier between
rp->rx_ring[entry].addr and rp->rx_ring[entry].rx_status updates to
enforce the ordering. The patch could help here as well.

You don't need to focus on rx_dropped: it's just a distraction :o)

Whatever the outcome I'll have to clean my mess though.

-- 
Ueimor
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