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

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Date:	Wed, 03 Jan 2007 08:25:48 -0600
From:	Steve Wise <swise@...ngridcomputing.com>
To:	"Michael S. Tsirkin" <mst@...lanox.co.il>
Cc:	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

> > @@ -1373,7 +1374,7 @@ int ib_peek_cq(struct ib_cq *cq, int wc_
> >  static inline int ib_req_notify_cq(struct ib_cq *cq,
> >  				   enum ib_cq_notify cq_notify)
> >  {
> > -	return cq->device->req_notify_cq(cq, cq_notify);
> > +	return cq->device->req_notify_cq(cq, cq_notify, NULL);
> >  }
> >  
> >  /**
> 
> Can't say I like this adding overhead in data path operations (and note this
> can't be optimized out). And kernel consumers work without passing it in, so it
> hurts kernel code even for Chelsio. Granted, the cost is small here, but these
> things do tend to add up.
> 
> It seems all Chelsio needs is to pass in a consumer index - so, how about a new
> entry point? Something like void set_cq_udata(struct ib_cq *cq, struct ib_udata *udata)?
> 

Adding a new entry point would hurt chelsio's user mode performance if
if then requires 2 kernel transitions to rearm the cq.  

Passing in user data is sort of SOP for these sorts of verbs.  

How much does passing one more param cost for kernel users?  



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