netdev - Re: [RFC] net: remove busylock

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Message-ID: <1463686523.18194.232.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Thu, 19 May 2016 12:35:23 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Duyck <alexander.duyck@...il.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Alexander Duyck <aduyck@...antis.com>
Subject: Re: [RFC] net: remove busylock

On Thu, 2016-05-19 at 11:56 -0700, Eric Dumazet wrote:

> Removing busylock helped in all cases I tested. (at least on x86 as
> David pointed out)
> 
> As I said, we need to revisit busylock now that spinlocks are different.
> 
> In one case (20 concurrent UDP netperf), I even got a 500 % increase.
> 
> With busylock :
> 
> lpaa5:~# sar -n DEV 4 4|grep eth0
> Average:         eth0     12.19 112797.12      1.95  37672.28      0.00      0.00      0.69
> 


Hmpf, my sysctl logic was inverted. Really these results made little
sense.

Sorry for the noise. At least we have 8% confirmed gain with this
stuff ;)

> Presumably it would tremendously help if the actual kfree_skb()
> was done after qdisc lock is released, ie not from the qdisc->enqueue()
> method.
> 

This part is still valid.

We could have a per cpu storage of one skb pointer, so that we do not
have to change all ->enqueue() prototypes.