netdev - Re: RFS issue: no HW filter for paused stream

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Date:	Mon, 19 Sep 2011 09:05:08 +0300
From:	Amir Vadai <amirv@....mellanox.co.il>
To:	Tom Herbert <therbert@...gle.com>
Cc:	oren@...lanox.co.il, liranl@...lanox.co.il, netdev@...r.kernel.org,
	amirv@...lanox.co.il
Subject: Re: RFS issue: no HW filter for paused stream

(Resending in plain text)

Tom Hi,
When a stream is paused, and its rule is expired while it is paused,
no new rule will be configured to the HW when traffic resume.

Scenario:
1. Start iperf.
2. Pause it using Ctrl-Z
3. Start another iperf (to make sure first stream rule is expired)
4. Stop the second stream.
5. Resume first stream. Traffic is not steered to the right rx-queue.

>From looking at the code:
- When first stream started, RSS steered traffic to rx-queue 'x'.
Because iperf server was running on a different CPU, a new rule was
added and current-cpu was set to desired-cpu.
- After paused, rule was expired and removed from HW by net driver.
But current-cpu wasn't cleared and still is equal to desired-cpu.
- When stream was resumed, traffic was steered again by RSS, and
because current-cpu was equal to desired-cpu,  ndo_rx_flow_steer
wasn't called and no rule was configured to the HW.

Why isn't current-cpu cleared when expiring a rule?
- Amir
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