netdev - Re: [PATCH net-next] dql: dql_queued() should write first to reduce bus transactions

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Message-ID: <1411732975.16953.106.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 26 Sep 2014 05:02:55 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
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>
Subject: Re: [PATCH net-next] dql: dql_queued() should write first to reduce
 bus transactions

On Fri, 2014-09-26 at 13:06 +0200, Hannes Frederic Sowa wrote:

> I thought that prefetchw() would be the canonical way to solve write
> stalls in CPUs and prepare the specific cache line to be written to.
> Interesting, thanks Eric.

True, and I have a tcp_ack() (tcp_clean_rtx_queue() more exactly) patch
that indeed uses prefetchw() to bring tcp_shinfo() in cache before the 
tcp_unlink_write_queue(skb, sk);

Performance went from 570000 packets per second to 820000 packets per
second on a TSO=off GSO=off workload.

But this applies after the https://patchwork.ozlabs.org/patch/392877/
patch (tcp: change tcp_skb_pcount() location )



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