[openib-general] [PATCH][1/7]ipoib performance patches -- remove ah_reap

[Shirley Ma]

Roland Dreier <rdreier at cisco.com> wrote on 05/24/2006 01:50:37 PM:

> NAK to this patch.  Not only is is a step backwards in performance --
> you've essentially added two (expensive) atomic operations for every
> packet sent 

My observation is the atomic operation is not that expensive.

> -- but the patch is actually wrong:
> 
>  > +       err = post_send(priv, priv->tx_head & (ipoib_sendq_size - 1), 

>  > +                       address->ah, qpn, addr, skb->len); 
>  > +       kref_put(&address->ref, ipoib_free_ah);
> 
> The whole point of the complexity in AH handling in IPoIB is that AHs
> cannot be freed until the driver knows that all sends referring to
> them have _completed_.  As you've written your patch, an AH can easily
> be freed before the HCA has a chance to execute the corresponding send
> request.
> 
>  - R.

I thought the path holding another AH reference to prevent it to be freed?

Thanks
Shirley Ma
IBM Linux Technology Center
15300 SW Koll Parkway
Beaverton, OR 97006-6063
Phone(Fax): (503) 578-7638




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