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

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Date:	Wed, 21 Sep 2011 16:09:02 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	amirv@...lanox.co.il
Cc:	Tom Herbert <therbert@...gle.com>, oren@...lanox.co.il,
	liranl@...lanox.co.il, netdev@...r.kernel.org,
	Diego Crupnicoff <Diego@...lanox.com>
Subject: Re: RFS issue: no HW filter for paused stream

On Tue, 2011-09-20 at 09:53 +0300, Amir Vadai wrote:
> This will unset the current CPU of the rflow that belongs to the desired 
> CPU.
> The problem is when the stream resumes and it goes to the wrong RXQ - in 
> our HW, it will be according to RSS, as long as there is no specific 
> flow steering rule for the stream.

Sorry, yes.  Told you I didn't test my patch!

> We need to unset the current CPU of the rflow of the actual RXQ that the 
> packet arrived at:
[...]
> Or even better, not set it in the first place - but I'm not sure I 
> undersdtand the implications on RPS:
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 4b9981c..748acdb 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2654,7 +2654,7 @@ set_rps_cpu(struct net_device *dev, struct sk_buff 
> *skb,
>   {
>          u16 tcpu;
> 
> -   tcpu = rflow->cpu = next_cpu;
> + tcpu = next_cpu;
>          if (tcpu != RPS_NO_CPU) {
>   #ifdef CONFIG_RFS_ACCEL
>                  struct netdev_rx_queue *rxqueue;
> 
> 

But that means we never move the flow to a new CPU in the non-
accelerated case.  So maybe the proper change would be:

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2652,10 +2652,7 @@ static struct rps_dev_flow *
 set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 	    struct rps_dev_flow *rflow, u16 next_cpu)
 {
-	u16 tcpu;
-
-	tcpu = rflow->cpu = next_cpu;
-	if (tcpu != RPS_NO_CPU) {
+	if (next_cpu != RPS_NO_CPU) {
 #ifdef CONFIG_RFS_ACCEL
 		struct netdev_rx_queue *rxqueue;
 		struct rps_dev_flow_table *flow_table;
@@ -2683,16 +2680,16 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 			goto out;
 		old_rflow = rflow;
 		rflow = &flow_table->flows[flow_id];
-		rflow->cpu = next_cpu;
 		rflow->filter = rc;
 		if (old_rflow->filter == rflow->filter)
 			old_rflow->filter = RPS_NO_FILTER;
 	out:
 #endif
 		rflow->last_qtail =
-			per_cpu(softnet_data, tcpu).input_queue_head;
+			per_cpu(softnet_data, next_cpu).input_queue_head;
 	}
 
+	rflow->cpu = next_cpu;
 	return rflow;
 }
 
--- END ---

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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