From: Bruce Richardson <bruce.richardson@intel.com>
To: "Xie, Huawei" <huawei.xie@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] virtio: fix rx ring descriptor starvation
Date: Wed, 10 Feb 2016 15:07:01 +0000 [thread overview]
Message-ID: <20160210150700.GA14232@bricha3-MOBL3> (raw)
In-Reply-To: <C37D651A908B024F974696C65296B57B4C574D68@SHSMSX101.ccr.corp.intel.com>
On Tue, Jan 05, 2016 at 07:13:04AM +0000, Xie, Huawei wrote:
> On 12/17/2015 7:18 PM, Tom Kiely wrote:
> >
> >
> > On 11/25/2015 05:32 PM, Xie, Huawei wrote:
> >> On 11/13/2015 5:33 PM, Tom Kiely wrote:
> >>> If all rx descriptors are processed while transient
> >>> mbuf exhaustion is present, the rx ring ends up with
> >>> no available descriptors. Thus no packets are received
> >>> on that ring. Since descriptor refill is performed post
> >>> rx descriptor processing, in this case no refill is
> >>> ever subsequently performed resulting in permanent rx
> >>> traffic drop.
> >>>
> >>> Signed-off-by: Tom Kiely <tkiely@brocade.com>
> >>> ---
> >>> drivers/net/virtio/virtio_rxtx.c | 6 ++++--
> >>> 1 file changed, 4 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/drivers/net/virtio/virtio_rxtx.c
> >>> b/drivers/net/virtio/virtio_rxtx.c
> >>> index 5770fa2..a95e234 100644
> >>> --- a/drivers/net/virtio/virtio_rxtx.c
> >>> +++ b/drivers/net/virtio/virtio_rxtx.c
> >>> @@ -586,7 +586,8 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf
> >>> **rx_pkts, uint16_t nb_pkts)
> >>> if (likely(num > DESC_PER_CACHELINE))
> >>> num = num - ((rxvq->vq_used_cons_idx + num) %
> >>> DESC_PER_CACHELINE);
> >>> - if (num == 0)
> >>> + /* Refill free descriptors even if no pkts recvd */
> >>> + if (num == 0 && virtqueue_full(rxvq))
> >> Should the return condition be that no used buffers and we have avail
> >> descs in avail ring, i.e,
> >> num == 0 && rxvq->vq_free_cnt != rxvq->vq_nentries
> >>
> >> rather than
> >> num == 0 && rxvq->vq_free_cnt == 0
> > Yes we could do that but I don't see a good reason to wait until the
> > vq_free_cnt == vq_nentries
> > before attempting the refill. The existing code will attempt refill
> > even if only 1 packet was received
> > and the free count is small. To me it seems safer to extend that to
> > try refill even if no packet was received
> > but the free count is non-zero.
> The existing code attempt to refill only if 1 packet was received.
>
> If we want to refill even no packet was received, then the strict
> condition should be
> num == 0 && rxvq->vq_free_cnt != rxvq->vq_nentries
>
> The safer condition, what you want to use, should be
> num == 0 && !virtqueue_full(...)
> rather than
> num == 0 && virtqueue_full(...)
>
> We could simplify things a bit, just remove this check, if the following
> receiving code already takes care of the "num == 0" condition.
>
> I find virtqueue_full is confusing, maybe we could change it to some
> other meaningful name.
>
> >
> > Tom
> >
Ping.
Tom and Huawei, what is the status of this patch? Will there be a V2?
/Bruce
next prev parent reply other threads:[~2016-02-10 15:07 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-13 9:30 Tom Kiely
2015-11-24 21:20 ` Thomas Monjalon
2015-11-25 1:50 ` Yuanhan Liu
2015-11-25 2:51 ` Xie, Huawei
2015-11-25 17:32 ` Xie, Huawei
[not found] ` <C37D651A908B024F974696C65296B57B4C545F75@SHSMSX101.ccr.corp.intel.com>
2015-12-17 9:22 ` Tom Kiely
2015-12-17 11:18 ` Tom Kiely
2016-01-05 7:13 ` Xie, Huawei
2016-02-10 15:07 ` Bruce Richardson [this message]
2016-02-18 14:03 ` Kyle Larose
2016-02-22 16:23 ` Tom Kiely
2016-02-23 8:26 ` Xie, Huawei
2016-03-04 6:16 ` Xie, Huawei
2016-03-04 8:11 ` Tom Kiely
2016-03-04 13:25 ` Kyle Larose
2016-03-09 21:37 ` Bruce Richardson
2016-03-10 14:46 ` Kyle Larose
2016-02-26 18:58 Kyle Larose
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