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Subject: Re: [PATCH 5/5] e1000e: Avoid receiver overrun interrupt bursts
From: Philip Prindeville <philipp_subx@redfish-solutions.com>
In-Reply-To: <20170721184848.GU18556@csclub.uwaterloo.ca>
Date: Fri, 11 Aug 2017 20:13:47 -0600
Cc: Benjamin Poirier <bpoirier@suse.com>,
        Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
        intel-wired-lan@lists.osuosl.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
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References: <20170721160937.GA22632@csclub.uwaterloo.ca>
 <20170721183627.13373-1-bpoirier@suse.com>
 <20170721183627.13373-5-bpoirier@suse.com>
 <20170721184848.GU18556@csclub.uwaterloo.ca>
To: Lennart Sorensen <lsorense@csclub.uwaterloo.ca>
Sender: linux-kernel-owner@vger.kernel.org
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> On Jul 21, 2017, at 12:48 PM, Lennart Sorensen <lsorense@csclub.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@csclub.uwaterloo.ca>
>> Fixes: 16ecba59bc33 ("e1000e: Do not read ICR in Other interrupt")
>> Signed-off-by: Benjamin Poirier <bpoirier@suse.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