netdev - Re: [PATCH net-next 5/9] net: network drivers no longer need to implement ndo_busy

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Date:	Tue, 17 Nov 2015 17:14:11 +0200
From:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
To:	Eric Dumazet <edumazet@...gle.com>,
	"David S . Miller" <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>, Eli Cohen <eli@...lanox.com>,
	Amir Vadai <amirv@...lanox.com>,
	Ariel Elior <ariel.elior@...gic.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Rida Assaf <rida@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next 5/9] net: network drivers no longer need to
 implement ndo_busy_poll()

On 17/11/2015 15:57, Eric Dumazet wrote:
> Instead of having to implement complex ndo_busy_poll() method,
> drivers can simply rely on NAPI poll logic.

I really like where you are going with this series.

...

> We could go one step further, and make busy polling
> available for all NAPI drivers, but this would require
> that all netif_napi_del() calls are done in process context
> so that we can call synchronize_rcu().
> Full audit would be required.
> 
> Before this is done, a driver still needs to call :
> 
> - skb_mark_napi_id() for each skb provided to the stack, although we can
>   easily do this directly in core networking stack in a future patch.
> 
> - napi_hash_add() and napi_hash_del() to allocate/free a napi_id per napi.
> 
> - Make sure RCU grace period is respected after napi_hash_del() before
>   memory containing napi structure is freed.

Can we move all of these into the NAPI infrastructure?
Maybe hash add/del can be inside netif_napi_add/del.
Some way to force the right RCU behavior, and busy polling is
completely driver-agnostic, which IMHO outweighs the small gains
you can have by micro-optimizing ndo_busy_poll.

On another note, any thoughts about unifying poll_controller with
regular poll?

cheers,
Eliezer

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