linux-kernel - Re: [MAINLINE 0/2] Enable DIM for legacy ULPs and use it in RDS

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Message-ID: <20240925092645.GD967758@unreal>
Date: Wed, 25 Sep 2024 12:26:45 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>
Cc: Haakon Bugge <haakon.bugge@...cle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Allison Henderson <allison.henderson@...cle.com>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	OFED mailing list <linux-rdma@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"rds-devel@....oracle.com" <rds-devel@....oracle.com>
Subject: Re: [MAINLINE 0/2] Enable DIM for legacy ULPs and use it in RDS

On Wed, Sep 25, 2024 at 10:04:21AM +0800, Zhu Yanjun wrote:
> 在 2024/9/24 23:16, Haakon Bugge 写道:
> > 
> > 
> > > On 24 Sep 2024, at 15:59, Zhu Yanjun <yanjun.zhu@...ux.dev> wrote:
> > > 
> > > 在 2024/9/24 14:54, Christoph Hellwig 写道:
> > > > On Tue, Sep 24, 2024 at 09:58:24AM +0800, Zhu Yanjun wrote:
> > > > > The users that I mentioned is not in the kernel tree.
> > > > And why do you think that would matter the slightest?
> > > 
> > > I noticed that the same cq functions are used. And I also made tests with this patch series. Without this patch series, dim mechanism will not be invoked.
> > 
> > Christoph alluded to say: Do not modify the old cq_create_cq() code in order to support DIM, it is better to change the ULP to use ib_alloc_cq(), and get DIM enabled that way.
> 
> Hi, Haakon
> 
> To be honest, I like your original commit that enable DIM for legacy ULPs
> because this can fix this problem once for all and improve the old
> ib_create_cq function.
> 
> The idea from Christoph will cause a lot of changes in ULPs. I am not very
> sure if these changes cause risks or not.
> 
> Thus, I prefer to your original commit. But I will follow the advice from
> Leon and Jason.

Christoph was very clear and he summarized our position very well. We
said similar thing to SMC folks in 2022 [1] and RDS is no different here.

So no, "old ib_create_cq" shouldn't be used by ULPs.

Thanks

[1] https://lore.kernel.org/netdev/YePesYRnrKCh1vFy@unreal/

> 
> Zhu Yanjun
> 
> > 
> > 
> > Thxs, Håkon
> > 
> 
>