netdev - Re: [PATCH 5/5] e1000e: Avoid receiver overrun interrupt bursts

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Message-Id: <49B1F3E9-2A99-4AD6-9574-FC3960E67A77@redfish-solutions.com>
Date:   Fri, 11 Aug 2017 20:13:47 -0600
From:   Philip Prindeville <philipp_subx@...fish-solutions.com>
To:     Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
Cc:     Benjamin Poirier <bpoirier@...e.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] e1000e: Avoid receiver overrun interrupt bursts


> On Jul 21, 2017, at 12:48 PM, Lennart Sorensen <lsorense@...lub.uwaterloo.ca> wrote:
> 
> On Fri, Jul 21, 2017 at 11:36:27AM -0700, Benjamin Poirier wrote:
>> When e1000e_poll() is not fast enough to keep up with incoming traffic, the
>> adapter (when operating in msix mode) raises the Other interrupt to signal
>> Receiver Overrun.
>> 
>> This is a double problem because 1) at the moment e1000_msix_other()
>> assumes that it is only called in case of Link Status Change and 2) if the
>> condition persists, the interrupt is repeatedly raised again in quick
>> succession.
>> 
>> Ideally we would configure the Other interrupt to not be raised in case of
>> receiver overrun but this doesn't seem possible on this adapter. Instead,
>> we handle the first part of the problem by reverting to the practice of
>> reading ICR in the other interrupt handler, like before commit 16ecba59bc33
>> ("e1000e: Do not read ICR in Other interrupt"). Thanks to commit
>> 0a8047ac68e5 ("e1000e: Fix msi-x interrupt automask") which cleared IAME
>> from CTRL_EXT, reading ICR doesn't interfere with RxQ0, TxQ0 interrupts
>> anymore. We handle the second part of the problem by not re-enabling the
>> Other interrupt right away when there is overrun. Instead, we wait until
>> traffic subsides, napi polling mode is exited and interrupts are
>> re-enabled.
>> 
>> Reported-by: Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
>> Fixes: 16ecba59bc33 ("e1000e: Do not read ICR in Other interrupt")
>> Signed-off-by: Benjamin Poirier <bpoirier@...e.com>
> 
> Any chance of this fix hitting -stable?  After all adapter reset under
> load is not nice.
> 


I tried this patch sequence and I’m seeing a 2% drop in throughput.  CPU utilization at softIRQ is also about 8% higher.  The previous single patch that went out to fix this problem had better performance.

This is on an Atom D525 with an 82574L and running 2 GB streams across a pair of interfaces with iperf3.

-Philip