netdev - Re: [PATCH net-next v2 02/12] eth: mvpp2: implement new RSS context API

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Message-ID: <52cbca9f-503f-25b4-aabf-461d09f41e9f@gmail.com>
Date: Tue, 6 Aug 2024 14:28:16 +0100
From: Edward Cree <ecree.xilinx@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 pabeni@...hat.com, dxu@...uu.xyz, przemyslaw.kitszel@...el.com,
 donald.hunter@...il.com, gal.pressman@...ux.dev, tariqt@...dia.com,
 willemdebruijn.kernel@...il.com, jdamato@...tly.com,
 marcin.s.wojtas@...il.com, linux@...linux.org.uk
Subject: Re: [PATCH net-next v2 02/12] eth: mvpp2: implement new RSS context
 API

On 05/08/2024 22:29, Jakub Kicinski wrote:
> On Mon, 5 Aug 2024 12:25:28 +0100 Edward Cree wrote:
>>> mvpp2 doesn't have a key for the hash, it defaults to
>>> an empty/previous indir table.  
>>
>> Given that, should this be after patch #6?  So as to make it
>>  obviously correct not to populate ethtool_rxfh_context_key(ctx)
>>  with the default context's key.
> 
> It's a bit different. Patch 6 is about devices which have a key but 
> the same key is used for all contexts. mvpp2 has no key at all
> even for context 0 (get_rxfh_key_size is not defined).

Oh, I see.  Clarify that in the commit message, perhaps?

>>> @@ -5750,6 +5792,7 @@ static const struct net_device_ops mvpp2_netdev_ops = {
>>>  
>>>  static const struct ethtool_ops mvpp2_eth_tool_ops = {
>>>  	.cap_rss_ctx_supported	= true,
>>> +	.rxfh_max_context_id	= MVPP22_N_RSS_TABLES,  
>>
>> Max ID is inclusive, not exclusive, so I think this should be
>>  MVPP22_N_RSS_TABLES - 1?
> 
> I totally did check this before sending:
> 
>  * @rxfh_max_context_id: maximum (exclusive) supported RSS context ID.  If this
>  *	is zero then the core may choose any (nonzero) ID, otherwise the core
>  *	will only use IDs strictly less than this value, as the @rss_context
>  *	argument to @create_rxfh_context and friends.
> 
> But you're right, the code acts as if it was inclusive :S

Mea culpa, clearly when I was porting to XArray I must have
 confused myself over this.

> Coincidentally, the default also appears exclusive:
> 
> 	u32 limit = ops->rxfh_max_context_id ?: U32_MAX;
> 
> U32_MAX can't be used, it has special meaning:
> 
> #define ETH_RXFH_CONTEXT_ALLOC		0xffffffff

Given that both the default and drivers look more reasonable
 with an exclusive than an inclusive limit (I assume most
 drivers with a limit will have an N, like mvpp2 does, rather
 than a MAX), I guess we should change the code to match the
 doc rather than the other way around.

> These seem like net-worthy fixes, no?

Yep, agreed.  I'll send a patch.