netdev - RE: [EXT] Re: [PATCH net] octeontx2-pf: Set maximum queue size to 16K

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Date: Fri, 4 Aug 2023 02:25:55 +0000
From: Ratheesh Kannoth <rkannoth@...vell.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sunil Kovvuri
 Goutham <sgoutham@...vell.com>,
        Geethasowjanya Akula <gakula@...vell.com>,
        Subbaraya Sundeep Bhatta <sbhatta@...vell.com>,
        Hariprasad Kelam
	<hkelam@...vell.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org"
	<kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>
Subject: RE: [EXT] Re: [PATCH net] octeontx2-pf: Set maximum queue size to 16K

> From: Alexander Lobakin <aleksander.lobakin@...el.com>
> Sent: Thursday, August 3, 2023 8:37 PM
> To: Ratheesh Kannoth <rkannoth@...vell.com>
> Subject: [EXT] Re: [PATCH net] octeontx2-pf: Set maximum queue size to 16K


> > These recycling will impact on performance, right ? else, why didn't page
> pool made this size as constant.
> 
> Page Pool doesn't need huge ptr_ring sizes to successfully recycle pages.
> Especially given that the recent PP optimizations made locking recycling
> happen much more rarely.
Got it. Thanks. 

> Re "size as constant" -- because lots of NICs don't need more than 256 or 512
> descriptors and it would be only a waste to create page_pools with huge
> ptr_rings for them. Queue sizes bigger than 1024 (ok, maybe
> 2048) is the moment when the linear scale stops working. That's why I
> believe that going out of [64, 2048] for page_pools doesn't make much
> sense.
So, will clamp to 2048 in page_pool_init() ? But it looks odd to me, as 
User requests > 2048,  but will never be aware that it is clamped to 2048.
Better do this clamping in Driver and print a warning  message ? 

-Ratheesh