netdev - Re: [PATCH RFC]: napi

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Date:	Wed, 25 Jul 2007 23:33:03 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"David Miller" <davem@...emloft.net>, netdev@...r.kernel.org
cc:	shemminger@...ux-foundation.org, jgarzik@...ox.com,
	hadi@...erus.ca, rusty@...tcorp.com.au
Subject: Re: [PATCH RFC]: napi_struct V4

David Miller wrote:

>  	/* run TX completion thread */
>  	if (sblk->idx[0].tx_consumer != tp->tx_cons) {
> -		tg3_tx(tp);
> +		netif_tx_lock(netdev);
> +		__tg3_tx(tp);
> +		netif_tx_unlock(netdev);
>

This will lead to more and longer lock contentions between
->hard_start_xmit() and ->poll() in the normal fast path.  Why
do we need to widen the scope of netif_tx_lock() in this case?

By not taking the netif_tx_lock() during tx completions until
the last moment and only when necessary improves the performance
substantially.

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