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

From: "Håkon Bugge" <haakon.bugge@oracle.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Hans Westgaard Ry <hans.westgaard.ry@oracle.com>,
	Doug Ledford <dledford@redhat.com>,
	Jack Morgenstein <jackm@dev.mellanox.co.il>,
	Daniel Jurgens <danielj@mellanox.com>,
	Parav Pandit <parav@mellanox.com>,
	Pravin Shedge <pravin.shedge4linux@gmail.com>,
	OFED mailing list <linux-rdma@vger.kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] IB/mad: Use ID allocator routines to allocate agent number
Date: Tue, 29 May 2018 18:16:14 +0200	[thread overview]
Message-ID: <A470D739-D0CD-42EE-9196-8E7610B6DAF4@oracle.com> (raw)
In-Reply-To: <20180529154922.GA18457@ziepe.ca>

> On 29 May 2018, at 17:49, Jason Gunthorpe <jgg@ziepe.ca> wrote:
> 
> 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.
> 
> There is no reason for this to be an ida, just do something like
> 
> mad_agent_priv->agent.hi_tid = atomic_inc_return(&ib_mad_client_id) & mad_agent_priv->ib_dev->tid_mask;
> 
> And have the driver set tid_mask to 3 bytes of 0xFF

The issue is that some of the mad agents are long-lived, so you will wrap and use the same TID twice.

Thxs, Håkon

> 
> And no sysctl.
> 
> Jason
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