[openib-general] [PATCH for-2.6.21] IPoIB/cm: improve small message bandwidth

[Michael S. Tsirkin]

> Quoting r. Or Gerlitz <ogerlitz at voltaire.com>:
> Subject: Re: [openib-general] [PATCH for-2.6.21] IPoIB/cm: improve small message bandwidth
> 
> Michael S. Tsirkin wrote:
> > Avoid overhead of freeing/reallocating and mapping/unmapping for dma
> > for pages that have not been written to by hardware.
> 
> > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> > index 8ee6f06..a23c8e3 100644
> > --- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> > +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> > @@ -68,14 +68,14 @@ struct ipoib_cm_id {
> >  static int ipoib_cm_tx_handler(struct ib_cm_id *cm_id,
> >  			       struct ib_cm_event *event);
> >  
> > -static void ipoib_cm_dma_unmap_rx(struct ipoib_dev_priv *priv,
> > +static void ipoib_cm_dma_unmap_rx(struct ipoib_dev_priv *priv, int frags,
> >  				  u64 mapping[IPOIB_CM_RX_SG])
> >  {
> >  	int i;
> >  
> >  	ib_dma_unmap_single(priv->ca, mapping[0], IPOIB_CM_HEAD_SIZE, DMA_FROM_DEVICE);
> >  
> > -	for (i = 0; i < IPOIB_CM_RX_SG - 1; ++i)
> > +	for (i = 0; i < frags; ++i)
> >  		ib_dma_unmap_single(priv->ca, mapping[i + 1], PAGE_SIZE, DMA_FROM_DEVICE);
> >  }
> 
> I understand that in ipoib_cm_alloc_rx_skb you call dma_map_page on 
> IPOIB_CM_RX_SG pages where here you call dma_unmap_single only $frags 
> times, correct?

No.

> does this means you are trashing the IOMMU etc etc of 
> the system?

I don't think so.


-- 
MST