Message-ID: <1361379597.8629.39.camel@jlt4.sipsolutions.net> (sfid-20130220_180054_444131_D4C10143)
Subject: Re: 3.7.8/amd64 full interrupt hangs due to iwlwifi under big nfs
 copies out
From: Johannes Berg <johannes@sipsolutions.net>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Marc MERLIN <marc@merlins.org>, David Miller <davem@davemloft.net>,
	Larry.Finger@lwfinger.net, bhutchings@solarflare.com,
	linux-wireless@vger.kernel.org, netdev@vger.kernel.org
Date: Wed, 20 Feb 2013 17:59:57 +0100
In-Reply-To: <1361379331.19353.189.camel@edumazet-glaptop> (sfid-20130220_175537_373410_F2F98F44)
References: <1333998672.3007.245.camel@edumazet-glaptop>
	 <20120409.153452.1284163346306246866.davem@davemloft.net>
	 <1334030180.13293.98.camel@edumazet-glaptop>
	 <20120410051127.GA32048@merlins.org>
	 <1334038263.2907.1.camel@edumazet-glaptop>
	 <20120411052733.GA17352@merlins.org> <20120715215935.GF24420@merlins.org>
	 <1342419529.3265.12217.camel@edumazet-glaptop>
	 <20120716151826.GA10586@merlins.org>
	 <1342455717.2830.14.camel@edumazet-glaptop>
	 <20130219040557.GB4778@merlins.org>
	 <1361251033.19353.120.camel@edumazet-glaptop>
	 (sfid-20130219_061917_530878_1ED7A14C) <1361268221.8553.1.camel@jlt4.sipsolutions.net>
	 <1361290909.19353.140.camel@edumazet-glaptop>
	 (sfid-20130219_172155_748777_C3ED0F5E) <1361351538.8629.3.camel@jlt4.sipsolutions.net>
	 (sfid-20130220_101252_930264_DBD3955C) <1361351703.8629.5.camel@jlt4.sipsolutions.net>
	 <1361373064.19353.180.camel@edumazet-glaptop>
	 (sfid-20130220_161110_395796_DBAC0744) <1361377243.8629.34.camel@jlt4.sipsolutions.net>
	 <1361379331.19353.189.camel@edumazet-glaptop>
	 (sfid-20130220_175537_373410_F2F98F44)
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Sender: linux-wireless-owner@vger.kernel.org

On Wed, 2013-02-20 at 08:55 -0800, Eric Dumazet wrote:

> > > It will make a huge difference, even on non pressure mode, as TCP
> > > receive window will grow twice faster.
> > 
> > Hmm, why does that depend on the allocation size?
> 
> I guess you missed all the patches about skb->truesize on netdev

Yeah, I don't follow netdev much any more...

> > > -	skb = alloc_skb(128, GFP_ATOMIC);
> > > +	fraglen = 128;
> > > +	/* if we use order-1 pages, copy to get better TCP performance */
> > > +	if (rxb->truesize > PAGE_SIZE)
> > > +		fraglen = max_t(unsigned, fraglen, len);
> > > +
> > > +	skb = alloc_skb(fraglen, GFP_ATOMIC);
> > 
> > Hmm, I don't quite understand -- that's not doing any copy?
> > 
> > FWIW if you do the copy you should not "steal" the pages, then they'd be
> > recycled in the RX ring right away.
> 
> Code should just works, please read the following lines in the same
> function....
> 
>         /* If frame is small enough to fit in skb->head, pull it completely.
>          * If not, only pull ieee80211_hdr so that splice() or TCP coalesce
>          * are more efficient.
>          */

Oh, right, though I guess the comment is now wrong since practically
every packet will be copied either here or in mac80211 (A-MSDUs are
split up there)

johannes