netdev - Re: [PATCH V2 net-next] liquidio: prevent rx queues from getting stalled

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Message-Id: <20180330.142100.1787650171524973056.davem@davemloft.net>
Date:   Fri, 30 Mar 2018 14:21:00 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     felix.manlunas@...ium.com
Cc:     netdev@...r.kernel.org, raghu.vatsavayi@...ium.com,
        derek.chickles@...ium.com, satananda.burla@...ium.com
Subject: Re: [PATCH V2 net-next] liquidio: prevent rx queues from getting
 stalled

From: Felix Manlunas <felix.manlunas@...ium.com>
Date: Thu, 29 Mar 2018 11:13:22 -0700

> From: Raghu Vatsavayi <raghu.vatsavayi@...ium.com>
> 
> This commit has fix for RX traffic issues when we stress test the driver
> with continuous ifconfig up/down under very high traffic conditions.
> 
> Reason for the issue is that, in existing liquidio_stop function NAPI is
> disabled even before actual FW/HW interface is brought down via
> send_rx_ctrl_cmd(lio, 0). Between time frame of NAPI disable and actual
> interface down in firmware, firmware continuously enqueues rx traffic to
> host. When interrupt happens for new packets, host irq handler fails in
> scheduling NAPI as the NAPI is already disabled.
> 
> After "ifconfig <iface> up", Host re-enables NAPI but cannot schedule it
> until it receives another Rx interrupt. Host never receives Rx interrupt as
> it never cleared the Rx interrupt it received during interface down
> operation. NIC Rx interrupt gets cleared only when Host processes queue and
> clears the queue counts. Above anomaly leads to other issues like packet
> overflow in FW/HW queues, backpressure.
> 
> Fix:
> This commit fixes this issue by disabling NAPI only after informing
> firmware to stop queueing packets to host via send_rx_ctrl_cmd(lio, 0).
> send_rx_ctrl_cmd is not visible in the patch as it is already there in the
> code. The DOWN command also waits for any pending packets to be processed
> by NAPI so that the deadlock will not occur.
> 
> Signed-off-by: Raghu Vatsavayi <raghu.vatsavayi@...ium.com>
> Acked-by: Derek Chickles <derek.chickles@...ium.com>
> Signed-off-by: Felix Manlunas <felix.manlunas@...ium.com>

Applied.