netdev - Re: [PATCH v4 01/13] Linux RDMA Core Changes

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Date:	Wed, 03 Jan 2007 09:07:21 -0600
From:	Steve Wise <swise@...ngridcomputing.com>
To:	"Michael S. Tsirkin" <mst@...lanox.co.il>
Cc:	Roland Dreier <rdreier@...co.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, openib-general@...nib.org
Subject: Re: [PATCH  v4 01/13] Linux RDMA Core Changes

On Wed, 2007-01-03 at 17:00 +0200, Michael S. Tsirkin wrote:
> > > 
> > > No, it won't need 2 transitions - just an extra function call,
> > > so it won't hurt performance - it would improve performance.
> > > 
> > > ib_uverbs_req_notify_cq would call
> > > 
> > > 	ib_uverbs_req_notify_cq()
> > > 	{
> > > 			ib_set_cq_udata(cq, udata)
> > > 			ib_req_notify_cq(cq, cmd.solicited_only ?
> > > 				IB_CQ_SOLICITED : IB_CQ_NEXT_COMP);
> > > 	}
> > > 
> > 
> > ib_set_cq_udata() would transition into the kernel to pass in the
> > consumer's index.  In addition, ib_req_notify_cq would also transition
> > into the kernel since its not a bypass function for chelsio.
> 
> We misunderstand each other.
> 
> ib_uverbs_req_notify_cq is in drivers/infiniband/core/uverbs_cmd.c -
> all this code runs inside the IB_USER_VERBS_CMD_REQ_NOTIFY_CQ command,
> so there is a single user to kernel transition.
> 

Oh I see. 

This seems like a lot of extra code to avoid passing one extra arg to
the driver's req_notify_cq verb.  I'd appreciate other folk's input on
how important they think this is.  

If you insist, then I'll run some tests specifically in kernel mode and
see how this affects mthca's req_notify performance.

Steve.





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