Re: [dpdk-dev] [PATCH] examples/vhost: use library routines instead of local copies

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: Zoltan Kiss [mailto:zoltan.kiss@linaro.org]
> Sent: Thursday, March 26, 2015 4:46 PM
> To: Ananyev, Konstantin; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] examples/vhost: use library routines instead of local copies
> 
> 
> 
> On 26/03/15 01:20, Ananyev, Konstantin wrote:
> >
> >
> >> -----Original Message-----
> >> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Zoltan Kiss
> >> Sent: Wednesday, March 25, 2015 6:43 PM
> >> To: dev@dpdk.org
> >> Cc: Zoltan Kiss
> >> Subject: [dpdk-dev] [PATCH] examples/vhost: use library routines instead of local copies
> >>
> >> This macro and function were copies from the mbuf library, no reason to keep
> >> them.
> >
> > NACK
> > You can't use RTE_MBUF_INDIRECT macro here.
> > If you'll look at vhost code carefully, you'll realise that we don't use standard rte_pktmbuf_attach() here.
> > As we attach mbuf not to another mbuf but to external memory buffer, passed to us by virtio device.
> > Look at attach_rxmbuf_zcp().
> Yes, I think the proper fix is to set the flag in attach_rxmbuf_zcp()
> and virtio_tx_route_zcp(), then you can use the library macro here.

No, it is not.
IND_ATTACHED_MBUF flag indicates that that mbuf attached to another mbuf and __rte_pktmbuf_prefree_seg()
would try to do mbuf detach.
We definetly don't want to set IND_ATTACHED_MBUF here.
I think there is no need to fix anything here.

Konstantin

> 
> > Though I suppose, we can replace pktmbuf_detach_zcp() , with  rte_pktmbuf_detach() - they are doing identical things.
> Yes, the only difference is that the latter do "m->ol_flags = 0" as well.
> 
> > BTW, I wonder did you ever  test your patch?
> Indeed I did not, shame on me. I don't have a KVM setup at hand. This
> fix were born as a side effect of the cleaning up in the library,
> and I'm afraid I don't have the time right now to create a KVM setup.
> Could anyone who has it at hand help out to run a quick test? (for the
> v2 of this patch, which I'll send in shortly)


> 
> Regards,
> 
> Zoltan
> 
> > My guess it would cause vhost with '--zero-copy' to crash or  corrupt the packets straightway.
> >
> > Konstantin
> >
> >>
> >> Signed-off-by: Zoltan Kiss <zoltan.kiss@linaro.org>
> >> ---
> >>   examples/vhost/main.c | 38 +++++---------------------------------
> >>   1 file changed, 5 insertions(+), 33 deletions(-)
> >>
> >> diff --git a/examples/vhost/main.c b/examples/vhost/main.c
> >> index c3fcb80..1c998a5 100644
> >> --- a/examples/vhost/main.c
> >> +++ b/examples/vhost/main.c
> >> @@ -139,8 +139,6 @@
> >>   /* Number of descriptors per cacheline. */
> >>   #define DESC_PER_CACHELINE (RTE_CACHE_LINE_SIZE / sizeof(struct vring_desc))
> >>
> >> -#define MBUF_EXT_MEM(mb)   (RTE_MBUF_FROM_BADDR((mb)->buf_addr) != (mb))
> >> -
> >>   /* mask of enabled ports */
> >>   static uint32_t enabled_port_mask = 0;
> >>
> >> @@ -1538,32 +1536,6 @@ attach_rxmbuf_zcp(struct virtio_net *dev)
> >>   	return;
> >>   }
> >>
> >> -/*
> >> - * Detach an attched packet mbuf -
> >> - *  - restore original mbuf address and length values.
> >> - *  - reset pktmbuf data and data_len to their default values.
> >> - *  All other fields of the given packet mbuf will be left intact.
> >> - *
> >> - * @param m
> >> - *   The attached packet mbuf.
> >> - */
> >> -static inline void pktmbuf_detach_zcp(struct rte_mbuf *m)
> >> -{
> >> -	const struct rte_mempool *mp = m->pool;
> >> -	void *buf = RTE_MBUF_TO_BADDR(m);
> >> -	uint32_t buf_ofs;
> >> -	uint32_t buf_len = mp->elt_size - sizeof(*m);
> >> -	m->buf_physaddr = rte_mempool_virt2phy(mp, m) + sizeof(*m);
> >> -
> >> -	m->buf_addr = buf;
> >> -	m->buf_len = (uint16_t)buf_len;
> >> -
> >> -	buf_ofs = (RTE_PKTMBUF_HEADROOM <= m->buf_len) ?
> >> -			RTE_PKTMBUF_HEADROOM : m->buf_len;
> >> -	m->data_off = buf_ofs;
> >> -
> >> -	m->data_len = 0;
> >> -}
> >>
> >>   /*
> >>    * This function is called after packets have been transimited. It fetchs mbuf
> >> @@ -1590,8 +1562,8 @@ txmbuf_clean_zcp(struct virtio_net *dev, struct vpool *vpool)
> >>
> >>   	for (index = 0; index < mbuf_count; index++) {
> >>   		mbuf = __rte_mbuf_raw_alloc(vpool->pool);
> >> -		if (likely(MBUF_EXT_MEM(mbuf)))
> >> -			pktmbuf_detach_zcp(mbuf);
> >> +		if (likely(RTE_MBUF_INDIRECT(mbuf)))
> >> +			rte_pktmbuf_detach(mbuf);
> >>   		rte_ring_sp_enqueue(vpool->ring, mbuf);
> >>
> >>   		/* Update used index buffer information. */
> >> @@ -1653,8 +1625,8 @@ static void mbuf_destroy_zcp(struct vpool *vpool)
> >>   	for (index = 0; index < mbuf_count; index++) {
> >>   		mbuf = __rte_mbuf_raw_alloc(vpool->pool);
> >>   		if (likely(mbuf != NULL)) {
> >> -			if (likely(MBUF_EXT_MEM(mbuf)))
> >> -				pktmbuf_detach_zcp(mbuf);
> >> +			if (likely(RTE_MBUF_INDIRECT(mbuf)))
> >> +				rte_pktmbuf_detach(mbuf);
> >>   			rte_ring_sp_enqueue(vpool->ring, (void *)mbuf);
> >>   		}
> >>   	}
> >> @@ -2149,7 +2121,7 @@ switch_worker_zcp(__attribute__((unused)) void *arg)
> >>   					}
> >>   					while (likely(rx_count)) {
> >>   						rx_count--;
> >> -						pktmbuf_detach_zcp(
> >> +						rte_pktmbuf_detach(
> >>   							pkts_burst[rx_count]);
> >>   						rte_ring_sp_enqueue(
> >>   							vpool_array[index].ring,
> >> --
> >> 1.9.1
> >