netdev - Re: virt-manager broken by bind(0) in net-next.

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Message-ID: <4984252B.8080508@cosmosbay.com>
Date:	Sat, 31 Jan 2009 11:17:15 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Evgeniy Polyakov <zbr@...emap.net>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	Herbert Xu <herbert@...dor.apana.org.au>, berrange@...hat.com,
	et-mgmt-tools@...hat.com, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: virt-manager broken by bind(0) in net-next.

Evgeniy Polyakov a écrit :
> On Sat, Jan 31, 2009 at 10:49:00AM +0100, Eric Dumazet (dada1@...mosbay.com) wrote:
>> It appears you are always right, I have nothing to say then.
>>
>> Stupid I am.
>>
>> I vote for plain revert of your initial patch, since you are anaware
>> of performance problems it introduces. Then, probably nobody cares
>> of my complaints, so dont worry.
> 
> Eric, do not get it soo personally :) After all it is only a matter of
> how we enjoy the process and have fun with the development.
> 
> Really, I appreciate your work and help, and likely this
> misunderstanding happened because of a bad mix of the original bug and
> this performance implication. Original bug has really nothing with what
> we discuss here. And while the performance problem with bound sockets
> creation may be visible, I did not observe it, while the idea
> implemented with this approach shows up clearly in the graph I posted.
> So I vote by both hands to further improve it by moving things around so
> that there would be no unneded cache flushes during update of this
> field.
> 

OK OK, as I said, dont worry, it was not a strong feeling from me, only
a litle bit upset, thats all.

We only need to know if the *fix* is solving Stephen problem

About performance effects of careful variable placement and percpu counter
strategy you might consult as an example :

http://lkml.indiana.edu/hypermail/linux/kernel/0812.1/01624.html

Now, with these patches applied, try to see effect of your new bsockets field
on a network workload doing lot of socket bind()/unbind() calls...

With current kernels, you probably wont notice because of inode/dcache hot
cache lines, but it might change eventually...


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