linux-kernel - RE: [Patch v8 12/12] RDMA/mana_ib: Add a driver for Microsoft Azure Network Adapter

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Message-ID: <SA0PR15MB3919DE8DE2C407D8E8A07E1F992D9@SA0PR15MB3919.namprd15.prod.outlook.com>
Date:   Fri, 21 Oct 2022 14:36:04 +0000
From:   Bernard Metzler <BMT@...ich.ibm.com>
To:     Tom Talpey <tom@...pey.com>, Long Li <longli@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "shiraz.saleem@...el.com" <shiraz.saleem@...el.com>,
        Ajay Sharma <sharmaajay@...rosoft.com>
CC:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: RE: [Patch v8 12/12] RDMA/mana_ib: Add a driver for Microsoft Azure Network
 Adapter



> -----Original Message-----
> From: Tom Talpey <tom@...pey.com>
> Sent: Friday, 21 October 2022 16:34
> To: Long Li <longli@...rosoft.com>; Bernard Metzler <BMT@...ich.ibm.com>;
> KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang <haiyangz@...rosoft.com>;
> Stephen Hemminger <sthemmin@...rosoft.com>; Wei Liu <wei.liu@...nel.org>;
> Dexuan Cui <decui@...rosoft.com>; David S. Miller <davem@...emloft.net>;
> Jakub Kicinski <kuba@...nel.org>; Paolo Abeni <pabeni@...hat.com>; Jason
> Gunthorpe <jgg@...pe.ca>; Leon Romanovsky <leon@...nel.org>;
> edumazet@...gle.com; shiraz.saleem@...el.com; Ajay Sharma
> <sharmaajay@...rosoft.com>
> Cc: linux-hyperv@...r.kernel.org; netdev@...r.kernel.org; linux-
> kernel@...r.kernel.org; linux-rdma@...r.kernel.org
> Subject: [EXTERNAL] Re: [Patch v8 12/12] RDMA/mana_ib: Add a driver for
> Microsoft Azure Network Adapter
> 
> On 10/20/2022 4:42 PM, Long Li wrote:
> >> [Bernard wrote...]
> 
> >>> +	props->max_qp_wr = MAX_SEND_BUFFERS_PER_QUEUE;
> >>> +
> >>> +	/*
> >>> +	 * max_cqe could be potentially much bigger.
> >>> +	 * As this version of driver only support RAW QP, set it to the same
> >>> +	 * value as max_qp_wr
> >>> +	 */
> >>> +	props->max_cqe = MAX_SEND_BUFFERS_PER_QUEUE;
> >>> +
> >>> +	props->max_mr_size = MANA_IB_MAX_MR_SIZE;
> >>> +	props->max_mr = INT_MAX;
> >>
> >> How the 24 bit wide MR keys can handle INT_MAX unique
> >> MR's?
> >
> > Not sure if I understand this correctly, lkey and rkey are u32 in ib_mr.
> 
> The upper 8 bits of an ib_mr remote token are reserved for use as a
> rotating key, this allows a consumer to more safely reuse an ib_mr
> without having to overallocate large region pools.
> 
> Tom.

Right, my point was that one cannot encode INT_MAX different MR 
identifiers into 32 - 8 = 24 bits.

Best,
Bernard.