linux-kernel - Re: [E1000-devel] e1000 1sec latency problem

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Message-ID: <47AB5419.6020309@qualcomm.com>
Date:	Thu, 07 Feb 2008 10:55:21 -0800
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	"Kok, Auke" <auke-jan.h.kok@...el.com>
CC:	Pavel Machek <pavel@....cz>, e1000-devel@...ts.sourceforge.net,
	jesse.brandeburg@...el.com,
	kernel list <linux-kernel@...r.kernel.org>,
	john.ronciak@...el.com, jeffrey.t.kirsher@...el.com
Subject: Re: [E1000-devel] e1000 1sec latency problem

Kok, Auke wrote:
> Max Krasnyansky wrote:
>> Kok, Auke wrote:
>>> Max Krasnyansky wrote:
>>>> Kok, Auke wrote:
>>>>> Max Krasnyansky wrote:
>>>>>> So you don't think it's related to the interrupt coalescing by any chance ?
>>>>>> I'd suggest to try and disable the coalescing and see if it makes any difference.
>>>>>> We've had lots of issues with coalescing misbehavior. Not this bad (ie 1 second) though.
>>>>>>
>>>>>> Add this to modprobe.conf and reload e1000 module
>>>>>>
>>>>>> options e1000 RxIntDelay=0,0 RxAbsIntDelay=0,0 InterruptThrottleRate=0,0 TxIntDelay=0,0 TxAbsIntDelay=0,0
>>>>> that can't be the problem. irq moderation would only account for 2-3ms variance
>>>>> maximum.
>>>> Oh, I've definitely seen worse than that. Not as bad as a 1second though. Plus you're talking
>>>> about the case when coalescing logic is working as designed ;-). What if there is some kind of 
>>>> bug where timer did not expire or something.
>>> we don't use a software timer in e1000 irq coalescing/moderation, it's all in
>>> hardware, so we don't have that problem at all. And I certainly have never seen
>>> anything you are referring to with e1000 hardware, and I do not know of any bug
>>> related to this.
>>>
>>> are you maybe confused with other hardware ?
>>>
>>> feel free to demonstrate an example...
>> Just to give you a background. I wrote and maintain http://libe1000.sf.net
>> So I know E1000 HW and SW in and out.
> 
> wow, even I do not dare to say that!
Ok maybe that was a bit of an overstatement :). 

>> And no I'm not confused with other HW and I know that we're
>> not using SW timers for the coalescing. HW can be buggy as well. Note that I'm not saying that I
>> know for sure that the problem is coalescing, I'm just suggesting to take it out of the equation
>> while Pavel is investigating.
>>
>> Unfortunately I cannot demonstrate an example but I've seen unexplained packet delays in the range 
>> of 1-20 milliseconds on E1000 HW (and boy ... I do have a lot of it in my labs). Once coalescing 
>> was disabled those problems have gone away.
> 
> this sounds like you have some sort of PCI POST-ing problem and those can indeed
> be worse if you use any form of interrupt coalescing. In any case that is largely
> irrelevant to the in-kernel drivers, and as I said we definately have no open
> issues on that right now, and I really do not recollect any as well either (other
> than the issue of interference when both ends are irq coalescing)
I was actually talking about in kernel drivers. ie We were seeing delays with TIPC running over in
kernel E1000 driver. And no it was not a TIPC issue, everything worked fine with over TG3 and issues
went away when coalescing was disabled. 
Anyway, I think we can drop this subject.

Max


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