netdev - Re: commit 16ecba59 breaks 82574L under heavy load.

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Date:   Fri, 21 Jul 2017 11:27:09 -0400
From:   lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To:     Benjamin Poirier <bpoirier@...e.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: Re: commit 16ecba59 breaks 82574L under heavy load.

On Thu, Jul 20, 2017 at 04:44:55PM -0700, Benjamin Poirier wrote:
> Could you please test the following patch and let me know if it:
> 1) reduces the interrupt rate of the Other msi-x vector
> 2) avoids the link flaps
> or
> 3) logs some dmesg warnings of the form "Other interrupt with unhandled [...]"
> In this case, please paste icr values printed.

I will give it a try.

Another odd behaviour I see is that the driver will hang in
napi_synchronize on shutdown if there is traffic at the time (at least
I think that's the trigger, maybe the trigger is if there has been an
overload of traffic and the backlog in napi was used).

>From doing some searching, this seems to be a problem that has plagued
some people for years with this driver.

I am having trouble figuring out exactly what napi_synchronize is waiting
for and who is supposed to toggle the flag it is waiting on.  The flag
appears to work backwards from what I would have expected it to do.
I see lots of places that can set the bit, but only napi_enable seems
to clear it again, and I don't see how that would get called for all
the places that potentially set the bit.

-- 
Len Sorensen