netdev - RE: [net-next PATCH 1/1 V4] qdisc: bulk dequeue support for qdiscs with TCQ_F

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Message-ID: <1411738697.16953.124.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 26 Sep 2014 06:38:17 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Tom Herbert <therbert@...gle.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Toke Høiland-Jørgensen <toke@...e.dk>,
	Florian Westphal <fw@...len.de>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Dave Taht <dave.taht@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: RE: [net-next PATCH 1/1 V4] qdisc: bulk dequeue support for qdiscs
 with TCQ_F_ONETXQUEUE

On Fri, 2014-09-26 at 13:16 +0000, David Laight wrote:

> OTOH it looks as though there is a big hit if you read then write
> a non-present cache line.

Well, this is exactly what it is about. Welcome to the club.

This is a well known problem.

Look at following old commit :

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=3f9d35b9514da6757ca98831372518f9eeb71b33



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