netdev - Re: [PATCH] NET : rt_check_expire() can take a long time, add a cond

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Date:	Sat, 17 Nov 2007 17:23:37 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	"David S. Miller" <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH] NET : rt_check_expire() can take a long time, add a cond_resched()

Andi Kleen a écrit :
> Eric Dumazet <dada1@...mosbay.com> writes:
> 
>> So it may sound unnecessary but in the rt_check_expire() case, with a
>> loop potentially doing XXX.XXX iterations, being able to bypass the
>> function call is a clear win (in my bench case, 25 ms instead of 88
>> ms). Impact on I-cache is irrelevant here as this rt_check_expires()
> 
> Measuring what? And really milli-seconds? The number does not sound plausible 
> to me.

You know Andi, I have seen production servers that needed several seconds to 
perform the flush. When you have millions of entries on this table, can you 
imagine the number of memory transactions (including atomic ops) needed to 
flush them all ?

The 25.000.000 ns and 88.000.000 ns numbers where on an empty table, but large 
(16 MB of memory)


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