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

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Message-ID: <3B6A8BD9-76C0-464E-847D-615C93BBDCB9@oracle.com>
Date: Tue, 24 Sep 2024 08:59:16 +0000
From: Haakon Bugge <haakon.bugge@...cle.com>
To: Christoph Hellwig <hch@...radead.org>
CC: Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
        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 24 Sep 2024, at 09:01, Christoph Hellwig <hch@...radead.org> wrote:
> 
> On Fri, Sep 20, 2024 at 06:51:18AM -0700, Christoph Hellwig wrote:
>> On Fri, Sep 20, 2024 at 09:46:06AM +0000, Haakon Bugge wrote:
>>>> I would much prefer if you could move RDS off that horrible API finally
>>>> instead of investing more effort into it and making it more complicated.
>>> 
>>> ib_alloc_cq() and family does not support arming the CQ with the IB_CQ_SOLICITED flag, which RDS uses.
>> 
>> Then work on supporting it.  RDS and SMC are the only users, so one
>> of the maintainers needs to drive it.
> 
> I took a quick look at what it would take, and adding IB_CQ_SOLICITED
> support to the cq API looks pretty trivial, you'll just need to pass
> it to ib_cq_pool_get by adding a new argument and the pass it
> down to __ib_alloc_cq.  So yes, please get started at moving RDS out
> of the stone age.

Agree. I'll work on that. I am also inclined to improve it by having designated CPUs where the worker threads polling the CQs execute, as that often improves cache hit rates. But that will come as another commit.


Thxs, Håkon