linux-kernel - Re: [PATCH 2/2] IB/mad: Use IDR for agent IDs

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Message-ID: <20180613073653.GC3275@mtr-leonro.mtl.com>
Date:   Wed, 13 Jun 2018 10:36:53 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, hans.westgaard.ry@...cle.com,
        Doug Ledford <dledford@...hat.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        linux-rdma@...r.kernel.org,
        Håkon Bugge <haakon.bugge@...cle.com>,
        Parav Pandit <parav@...lanox.com>,
        Jack Morgenstein <jackm@....mellanox.co.il>,
        Pravin Shedge <pravin.shedge4linux@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] IB/mad: Use IDR for agent IDs

On Tue, Jun 12, 2018 at 05:07:39PM -0700, Matthew Wilcox wrote:
> On Tue, Jun 12, 2018 at 02:33:22PM -0600, Jason Gunthorpe wrote:
> > > @@ -377,13 +378,24 @@ struct ib_mad_agent *ib_register_mad_agent(struct ib_device *device,
> > >  		goto error4;
> > >  	}
> > >
> > > -	spin_lock_irq(&port_priv->reg_lock);
> > > -	mad_agent_priv->agent.hi_tid = atomic_inc_return(&ib_mad_client_id);
> > > +	idr_preload(GFP_KERNEL);
> > > +	idr_lock(&ib_mad_clients);
> > > +	ret2 = idr_alloc_cyclic(&ib_mad_clients, mad_agent_priv, 0,
> > > +			(1 << 24), GFP_ATOMIC);
> >
> > I like this series, my only concern is this magic number here, at the
> > very least it deserves a big comment explaining why it
> > exists..
>
> Yes, you're right.  Maybe something like this ...
>
> /*
>  * The mlx4 driver uses the top byte to distinguish which virtual function
>  * generated the MAD, so we must avoid using it.
>  */
> #define AGENT_ID_LIMIT		(1 << 24)
>
> ...
>
> 	ret2 = idr_alloc_cyclic(&ib_mad_clients, mad_agent_priv, 0,
> 			AGENT_ID_LIMIT, GFP_ATOMIC);
>
> > Let me see if I can get someone to give it some test time, I assume
> > you haven't been able to test it it?
>
> I don't have any IB hardware.  Frankly I'm scared of Infiniband ;-)

I took it for regression, reliable results will be after -rc1 only.

Thanks

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