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

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Date:	Mon, 19 Sep 2011 08:13:33 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Amir Vadai <amirv@....mellanox.co.il>
Cc:	oren@...lanox.co.il, liranl@...lanox.co.il, netdev@...r.kernel.org,
	amirv@...lanox.co.il, Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: RFS issue: no HW filter for paused stream

Ben:  Once a accel RFS flow expires (because flow is idle?), how
should it get re-instantiated if thread's CPU doesn't change?

Tom

On Sun, Sep 18, 2011 at 11:05 PM, Amir Vadai <amirv@....mellanox.co.il> wrote:
> (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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