netdev - Re: 3.7.8/amd64 full interrupt hangs due to iwlwifi under big nfs copies out

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Message-ID: <1361390290.8579.4.camel@jlt4.sipsolutions.net>
Date:	Wed, 20 Feb 2013 20:58:10 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Marc MERLIN <marc@...lins.org>, David Miller <davem@...emloft.net>,
	Larry.Finger@...inger.net, bhutchings@...arflare.com,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: 3.7.8/amd64 full interrupt hangs due to iwlwifi under big nfs
 copies out

On Wed, 2013-02-20 at 11:17 -0800, Eric Dumazet wrote:
> On Wed, 2013-02-20 at 19:16 +0100, Johannes Berg wrote:
> 
> > Yes and no. The current code doesn't pull in much data, not even the IP
> > header, so worst case it copies 14 bytes (ethernet header) in mac80211
> > to obtain alignment. By pulling in everything here, it later has to copy
> > everything again later to obtain alignment.
> 
> Can you give me pointers to the code doing that ?

Sure: net/mac80211/rx.c ~line 1900, look for #ifndef
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.

> On x86 we should not doing anything.

We don't do anything if CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is
defined.

johannes

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