Re: [PATCH net-next v1 06/11] page_pool: Coordinate refill with memory providers

[Björn Töpel]

Stanislav Fomichev <sdf.kernel@xxxxxxxxx> writes:

> On 11/10, Björn Töpel wrote:

>> diff --git a/include/net/netdev_rx_queue.h b/include/net/netdev_rx_queue.h
>> index 989120cbf452..ca12cbf7b825 100644
>> --- a/include/net/netdev_rx_queue.h
>> +++ b/include/net/netdev_rx_queue.h
>> @@ -33,6 +33,12 @@ struct netdev_rx_queue {
>>  	struct pp_memory_provider_params mp_params;
>>  	/* stamps the page pools of each queue allocation */
>>  	u32				mp_gen;
>> +	/* NAPI of the running queue, for memory provider wakeups. Set while
>> +	 * mp_armed, and if the provider has a refill_done op. Written under
>> +	 * the ops lock, read under RCU, see netif_mp_wake().
>> +	 */
>> +	struct napi_struct __rcu	*mp_napi;
>> +	bool				mp_armed;
>
> The comment should explain why mp_napi != napi? (I do not understand why)

Fair. It's the same NAPI, with other rules. napi is the driver's
association: read under the ops lock, and not cleared when the NAPI is
deleted. Provider wakeups run without that lock, from socket syscalls
and ->release_netmem().

mp_napi is an RCU copy, set only while the device is up and the queue
isn't restarting, for providers with ->refill_done(). netif_napi_del()
clears it before its grace period. Setting it also schedules the NAPI
once, which replays wakeups lost while the queue was stopped. I'll put
that in the comment.


Björn