linux-kernel - Re: E1000: e1000_update

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Message-ID: <47CF17F7.4030405@nortel.com>
Date:	Wed, 05 Mar 2008 16:00:23 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	"Kok, Auke" <auke-jan.h.kok@...el.com>
CC:	Todd Tomaino <ttomaino@...ulet.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: E1000:   e1000_update_stats()

Kok, Auke wrote:

> the update_stats function is only called every two seconds, and scheduled once. I
> think that the chance that two of these functions run in contention in the way you
> point out are practically zero, and if they do then we have much bigger problems
> than just counters being wrong...

I recently did an investigation that ended up sampling a subset of those 
stats every millisecond (to get an accurate picture of how many packets 
were being arriving vs being dropped due to rx_fifo errors over short 
intervals).  Ultimately it turned out that we had very bursty traffic. 
So it's not entirely unheard-of to sample at much higher rates.

At the very least, if we're going to remove the atomicity of reading 
registers and updating stats, how about adding a comment to this effect 
in the code?

Chris
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