linux-kernel - Re: [patch] forcedeth: fix the NAPI poll function

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Date:	Tue, 16 Oct 2007 12:52:36 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, shemminger@...ux-foundation.org
Subject: Re: [patch] forcedeth: fix the NAPI poll function

Ingo Molnar wrote:
> * Jeff Garzik <jeff@...zik.org> wrote:
> 
>>> FYI, looks good so far, ontop of Linus' latest -git tree.
>>>
>>> btw., one thing i always found weird about forcedeth is that it 
>>> generates an extra ~100 irqs per second even when there's no network 
>>> traffic:
>>>
>>> 11:      89752    XT-PIC-XT        eth0
>>> 11:      89854    XT-PIC-XT        eth0
>>> 11:      89955    XT-PIC-XT        eth0
>>> 11:      90056    XT-PIC-XT        eth0
>>> 11:      90157    XT-PIC-XT        eth0
>>>
>>> (irq count snapshot every second). Just in case it's easy to fix ...
>>
>> May I presume that behavior occurs in both mainline and my fe-lock 
>> branch?
> 
> correct.

Any chance of getting a quick comparison of forcedeth CPU usage in your 
setup, between old driver and fe-lock driver?

I'm curious about the effects of fe-lock on CPU usage, which NAPI is 
known to perturb (in positive or negative directions, depending on 
conditions).

I presume both drivers can work at wire speed, sans any "too many 
iterations" problems...


>> That is likely the NIC's timer irq, which is programmed to kick the 
>> irq handler every so often.  DEV_NEED_TIMERIRQ is a starting point, as 
>> well as "Known bugs" at the top of forcedeth.c, if you're curious.
>>
>> I'm _betting_ that some of that can be eliminated, but we'll see...
> 
> ok. Was just a FYI - you were looking for feedback :-)

Thanks!  :)

	Jeff


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