Re: [dpdk-dev] [PATCH] net/i40e: fix unexpected mbuf free in vPMD

["Zhang, Qi Z" <qi.z.zhang@intel.com>]

Hi Konstantin:

> -----Original Message-----
> From: Ananyev, Konstantin
> Sent: Monday, October 9, 2017 8:44 PM
> To: Zhang, Qi Z <qi.z.zhang@intel.com>; Wu, Jingjing <jingjing.wu@intel.com>;
> Xing, Beilei <beilei.xing@intel.com>
> Cc: dev@dpdk.org; Zhang, Qi Z <qi.z.zhang@intel.com>; stable@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH] net/i40e: fix unexpected mbuf free in vPMD
> 
> Hi Zhang,
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Qi Zhang
> > Sent: Monday, October 9, 2017 9:54 AM
> > To: Wu, Jingjing <jingjing.wu@intel.com>; Xing, Beilei
> > <beilei.xing@intel.com>
> > Cc: dev@dpdk.org; Zhang, Qi Z <qi.z.zhang@intel.com>; stable@dpdk.org
> > Subject: [dpdk-dev] [PATCH] net/i40e: fix unexpected mbuf free in vPMD
> >
> > The patch reset tx queue sw_ring's mbuf to NULL after it is free in
> > i40_tx_free_bufs, this prevent same mbuf be free again in
> > i40e_dev_tx_queue_release. This fix follow the same implemenation of
> > non-vPMD.
> 
> Wonder why we can't change i40e_dev_tx_queue_release() instead, so it will
> only go through the TXDs that were really armed?
Yes we can, I've thought about this before the patch, but after I measure the performance impact, I saw less than 0.6% downgrade for single core performance.
So I think maybe a simple fix could be good enough and low risk and an improvement can be delivered later after carefully validate.

> Let say from txq->tx_next_dd - tx_rs_thresh - 1 till txq->tx_tail?
> Let say _ixgbe_tx_queue_release_mbufs_vec() works that way.

Yes, That's the same way I figured out, thanks for giving the detail instruction that confirm my thought :)
Now, I think my v2 can upgrade to this directly.

Thanks
Qi

> Then we probably can keep our runtime code intact.

> Konstantin
> 
> >
> > Fixes: b4669bb95038 ("i40e: add vector Tx")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>
> > ---
> >  drivers/net/i40e/i40e_rxtx_vec_common.h | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/net/i40e/i40e_rxtx_vec_common.h
> > b/drivers/net/i40e/i40e_rxtx_vec_common.h
> > index 39a6da0..ed51b4d 100644
> > --- a/drivers/net/i40e/i40e_rxtx_vec_common.h
> > +++ b/drivers/net/i40e/i40e_rxtx_vec_common.h
> > @@ -124,11 +124,13 @@ i40e_tx_free_bufs(struct i40e_tx_queue *txq)
> >  	  */
> >  	txep = &txq->sw_ring[txq->tx_next_dd - (n - 1)];
> >  	m = rte_pktmbuf_prefree_seg(txep[0].mbuf);
> > +	txep[0].mbuf = NULL;
> >  	if (likely(m != NULL)) {
> >  		free[0] = m;
> >  		nb_free = 1;
> >  		for (i = 1; i < n; i++) {
> >  			m = rte_pktmbuf_prefree_seg(txep[i].mbuf);
> > +			txep[i].mbuf = NULL;
> >  			if (likely(m != NULL)) {
> >  				if (likely(m->pool == free[0]->pool)) {
> >  					free[nb_free++] = m;
> > @@ -145,6 +147,7 @@ i40e_tx_free_bufs(struct i40e_tx_queue *txq)
> >  	} else {
> >  		for (i = 1; i < n; i++) {
> >  			m = rte_pktmbuf_prefree_seg(txep[i].mbuf);
> > +			txep[i].mbuf = NULL;
> >  			if (m != NULL)
> >  				rte_mempool_put(m->pool, m);
> >  		}
> > --
> > 2.9.5