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

[Bernard Metzler]

> -----Original Message-----
> From: Tom Talpey <tom@xxxxxxxxxx>
> Sent: Friday, 21 October 2022 16:34
> To: Long Li <longli@xxxxxxxxxxxxx>; Bernard Metzler <BMT@xxxxxxxxxxxxxx>;
> KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>;
> Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>; Wei Liu <wei.liu@xxxxxxxxxx>;
> Dexuan Cui <decui@xxxxxxxxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>;
> Jakub Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni <pabeni@xxxxxxxxxx>; Jason
> Gunthorpe <jgg@xxxxxxxx>; Leon Romanovsky <leon@xxxxxxxxxx>;
> edumazet@xxxxxxxxxx; shiraz.saleem@xxxxxxxxx; Ajay Sharma
> <sharmaajay@xxxxxxxxxxxxx>
> Cc: linux-hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; linux-rdma@xxxxxxxxxxxxxxx
> 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.