netdev - Re: [PATCH RFC] v1 expedited "big hammer" RCU grace periods

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Date:	Thu, 23 Apr 2009 08:47:02 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
	akpm@...ux-foundation.org, davem@...emloft.net,
	dada1@...mosbay.com, zbr@...emap.net, jeff.chua.linux@...il.com,
	paulus@...ba.org, laijs@...fujitsu.com, jengelh@...ozas.de,
	r000n@...0n.net, benh@...nel.crashing.org,
	mathieu.desnoyers@...ymtl.ca
Subject: Re: [PATCH RFC] v1 expedited "big hammer" RCU grace periods



On Thu, 23 Apr 2009, Paul E. McKenney wrote:
> 
> Hmmm...  I need to ask Jeff Chua what HZ he was running with.  Because if
> there was some read-side critical section soaking up 30 milliseconds,
> all that hammering will do is slow things down...

The original bug report comes from simply bootup:

  "I'm loading all the firewall rules during boot-up and this 6 secs 
   slowness is really not very nice to wait for."

IOW, the problematic case likely effectively has _nothing_ else going on. 
Sure, there might be some parallelism (the bootup scripts are getting 
better for that), but hopefully not 6 seconds worth, and not likely any 
complex critical sections.

		Linus
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