netdev - Re: [PATCH net-next] qdisc: validate skb without holding lock

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Message-Id: <20141003.153645.72976986956341944.davem@davemloft.net>
Date:	Fri, 03 Oct 2014 15:36:45 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	brouer@...hat.com, netdev@...r.kernel.org, therbert@...gle.com,
	hannes@...essinduktion.org, fw@...len.de, dborkman@...hat.com,
	jhs@...atatu.com, alexander.duyck@...il.com,
	john.r.fastabend@...el.com, dave.taht@...il.com, toke@...e.dk
Subject: Re: [PATCH net-next] qdisc: validate skb without holding lock

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 03 Oct 2014 15:31:07 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Validation of skb can be pretty expensive :
> 
> GSO segmentation and/or checksum computations.
> 
> We can do this without holding qdisc lock, so that other cpus
> can queue additional packets.
> 
> Trick is that requeued packets were already validated, so we carry
> a boolean so that sch_direct_xmit() can validate a fresh skb list,
> or directly use an old one.
> 
> Tested on 40Gb NIC (8 TX queues) and 200 concurrent flows, 48 threads
> host.
> 
> Turning TSO on or off had no effect on throughput, only few more cpu
> cycles. Lock contention on qdisc lock disappeared.
> 
> Same if disabling TX checksum offload.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thanks Eric!
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