netdev - Re: [PATCH net V1 1/3] net/mlx4_en: Don't use irq_affinity_notifier to track changes in IRQ affinity map

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Date:	Sun, 29 Jun 2014 23:41:51 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Amir Vadai <amirv@...lanox.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Yevgeny Petrilin <yevgenyp@...lanox.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ben Hutchings <ben@...adent.org.uk>
Subject: Re: [PATCH net V1 1/3] net/mlx4_en: Don't use irq_affinity_notifier
 to track changes in IRQ affinity map

On Sun, 2014-06-29 at 11:54 +0300, Amir Vadai wrote:
> IRQ affinity notifier can only have a single notifier - cpu_rmap
> notifier. Can't use it to track changes in IRQ affinity map.
> Detect IRQ affinity changes by comparing CPU to current IRQ affinity map
> during NAPI poll thread.

...

> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
> index 8be7483..ac3dead 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
> @@ -474,15 +474,9 @@ int mlx4_en_poll_tx_cq(struct napi_struct *napi, int budget)
>  	/* If we used up all the quota - we're probably not done yet... */
>  	if (done < budget) {
>  		/* Done for now */
> -		cq->mcq.irq_affinity_change = false;
>  		napi_complete(napi);
>  		mlx4_en_arm_cq(priv, cq);
>  		return done;
> -	} else if (unlikely(cq->mcq.irq_affinity_change)) {
> -		cq->mcq.irq_affinity_change = false;
> -		napi_complete(napi);
> -		mlx4_en_arm_cq(priv, cq);
> -		return 0;
>  	}
>  	return budget;
>  }

It seems nothing is done then for the TX side after this patch ?

You might want to drain whole queue instead of limiting to a 'budget',
otherwise, a cpu might be stuck servicing (soft)irq for the TX
completion, even if irq affinities say otherwise.




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