netdev - Re: [PATCH] net: allow netdev_wait

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Date:	Sun, 25 Oct 2009 09:35:10 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Octavian Purdila <opurdila@...acom.com>
CC:	paulmck@...ux.vnet.ibm.com, Benjamin LaHaise <bcrl@...et.ca>,
	netdev@...r.kernel.org, Cosmin Ratiu <cratiu@...acom.com>
Subject: Re: [PATCH] net: allow netdev_wait_allrefs() to run faster

Octavian Purdila a écrit :
> 
> Got some time today and did some experiments myself. The test is deleting 1000 
> dummy interfaces (interface status down, no IP/IPv6 addresses assigned) on a 
> UP non-preempt ppc750 @800Mhz system.
> 
> 1. Ben's patch:
> 
> real    0m 3.42s
> user    0m 0.00s
> sys     0m 0.00s
> 
> 2. Eric's schedule_timeout_uninterruptible(1);
> 
> real    0m 3.00s
> user    0m 0.00s
> sys     0m 0.00s
> 
> 3. Simple synchronize_rcu_expedited()
> 
> This doesn't seem to work well with the UP non-preempt case since 
> synchronize_rcu_expedited() is a noop in this case - turning 
> netdev_wait_allrefs() into a while(1) loop.
> 

Thanks for these numbers. I presume HZ value is 1000 on this platform ?

Could you give us your scripts so that we can use same "benchmark" ?

BTW, I found I could not use IPV6 with many devices on x86_32, because of
the huge per_cpu allocations (on IPV6, each device has percpu SNMP counters)


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