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

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Message-ID: <20180613000739.GA32191@bombadil.infradead.org>
Date:   Tue, 12 Jun 2018 17:07:39 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     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 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 ;-)

> > +#define idr_lock(idr)		xa_lock(&(idr)->idr_rt)
> > +#define idr_unlock(idr)		xa_unlock(&(idr)->idr_rt)
> > +#define idr_lock_irq(idr)	xa_lock_irq(&(idr)->idr_rt)
> > +#define idr_unlock_irq(idr)	xa_unlock_irq(&(idr)->idr_rt)
> > +#define idr_lock_irqsave(idr, flags) \
> > +				xa_lock_irqsave(&(idr)->idr_rt, flags)
> > +#define idr_unlock_irqrestore(idr, flags) \
> > +				xa_unlock_irqrestore(&(idr)->idr_rt, flags)
> > +
> 
> And you are Ok to take these through the rdma tree?

Yes, that's fine with me; I'm not planning on merging any IDR patches
this cycle.  Thanks!