linux-kernel - Re: [PATCH] IB/mad: Use ID allocator routines to allocate agent number

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Date:   Tue, 29 May 2018 11:54:59 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Hans Westgaard Ry <hans.westgaard.ry@...cle.com>
Cc:     Doug Ledford <dledford@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Hakon Bugge <haakon.bugge@...cle.com>,
        Jack Morgenstein <jackm@....mellanox.co.il>,
        Daniel Jurgens <danielj@...lanox.com>,
        Parav Pandit <parav@...lanox.com>,
        Pravin Shedge <pravin.shedge4linux@...il.com>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IB/mad: Use ID allocator routines to allocate agent
 number

On Tue, May 29, 2018 at 09:38:08AM +0200, Hans Westgaard Ry wrote:
> The agent TID is a 64 bit value split in two dwords.  The least
> significant dword is the TID running counter. The most significant
> dword is the agent number. In the CX-3 shared port model, the mlx4
> driver uses the most significant byte of the agent number to store the
> slave number, making agent numbers greater and equal to 2^24 (3 bytes)
> unusable.  The current codebase uses a variable which is incremented
> atomically for each new agent number giving too large agent numbers
> over time.  The IDA set of functions are used instead of the simple
> counter approach. This allows re-use of agent numbers. A sysctl
> variable is also introduced, to control the max agent number.

Why don't you simply limit this number per-driver? By default, any
variable is allowed and mlx4_ib will set something else.

What is the advantage of having sysctl?

Thanks

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