[dpdk-dev] [PATCH v1] ixgbe_pmd: forbid tx_rs_thresh above 1 for all NICs but 82598

Lu, Wenzhuo wenzhuo.lu at intel.com
Wed Aug 19 02:42:15 CEST 2015


Hi Helin,

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Vlad Zolotarov
> Sent: Friday, August 14, 2015 1:38 PM
> To: Zhang, Helin; dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v1] ixgbe_pmd: forbid tx_rs_thresh above 1 for
> all NICs but 82598
> 
> 
> 
> On 08/13/15 23:28, Zhang, Helin wrote:
> > Hi Vlad
> >
> > I don't think the changes are needed. It says in datasheet that the RS
> > bit should be set on the last descriptor of every packet, ONLY WHEN
> TXDCTL.WTHRESH equals to ZERO.
> 
> Of course it's needed! See below.
> Exactly the same spec a few lines above the place u've just quoted states:
> 
> "Software should not set the RS bit when TXDCTL.WTHRESH is greater than
> zero."
> 
> And since all three (3) ixgbe xmit callbacks are utilizing RS bit notation ixgbe PMD
> is actually not supporting any value of WTHRESH different from zero.
I think Vlad is right. We need to fix this issue. Any suggestion? If not, I'd like to ack this patch.

> 
> >
> > Regards,
> > Helin
> >
> >> -----Original Message-----
> >> From: Vlad Zolotarov [mailto:vladz at cloudius-systems.com]
> >> Sent: Thursday, August 13, 2015 11:07 AM
> >> To: dev at dpdk.org
> >> Cc: Zhang, Helin; Ananyev, Konstantin; avi at cloudius-systems.com; Vlad
> >> Zolotarov
> >> Subject: [dpdk-dev] [PATCH v1] ixgbe_pmd: forbid tx_rs_thresh above 1 for
> all
> >> NICs but 82598
> >>
> >> According to 82599 and x540 HW specifications RS bit *must* be set in the
> last
> >> descriptor of *every* packet.
> > There is a condition that if TXDCTL.WTHRESH equal to zero.
> 
> Right and ixgbe PMD requires this condition to be fulfilled in order to
> function. See above.
> 
> >
> >> This patch fixes the Tx hang we were constantly hitting with a seastar-based
> >> application on x540 NIC.
> > Could you help to share with us how to reproduce the tx hang issue, with using
> > typical DPDK examples?
> 
> Sorry. I'm not very familiar with the typical DPDK examples to help u
> here. However this is quite irrelevant since without this this patch
> ixgbe PMD obviously abuses the HW spec as has been explained above.
> 
> We saw the issue when u stressed the xmit path with a lot of highly
> fragmented TCP frames (packets with up to 33 fragments with non-headers
> fragments as small as 4 bytes) with all offload features enabled.
> 
> Thanks,
> vlad
> >
> >> Signed-off-by: Vlad Zolotarov <vladz at cloudius-systems.com>
> >> ---
> >>   drivers/net/ixgbe/ixgbe_ethdev.c |  9 +++++++++
> >>   drivers/net/ixgbe/ixgbe_rxtx.c   | 23 ++++++++++++++++++++++-
> >>   2 files changed, 31 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/net/ixgbe/ixgbe_ethdev.c
> >> b/drivers/net/ixgbe/ixgbe_ethdev.c
> >> index b8ee1e9..6714fd9 100644
> >> --- a/drivers/net/ixgbe/ixgbe_ethdev.c
> >> +++ b/drivers/net/ixgbe/ixgbe_ethdev.c
> >> @@ -2414,6 +2414,15 @@ ixgbe_dev_info_get(struct rte_eth_dev *dev,
> struct
> >> rte_eth_dev_info *dev_info)
> >>   		.txq_flags = ETH_TXQ_FLAGS_NOMULTSEGS |
> >>   				ETH_TXQ_FLAGS_NOOFFLOADS,
> >>   	};
> >> +
> >> +	/*
> >> +	 * According to 82599 and x540 specifications RS bit *must* be set on
> the
> >> +	 * last descriptor of *every* packet. Therefore we will not allow the
> >> +	 * tx_rs_thresh above 1 for all NICs newer than 82598.
> >> +	 */
> >> +	if (hw->mac.type > ixgbe_mac_82598EB)
> >> +		dev_info->default_txconf.tx_rs_thresh = 1;
> >> +
> >>   	dev_info->hash_key_size = IXGBE_HKEY_MAX_INDEX * sizeof(uint32_t);
> >>   	dev_info->reta_size = ETH_RSS_RETA_SIZE_128;
> >>   	dev_info->flow_type_rss_offloads = IXGBE_RSS_OFFLOAD_ALL; diff --
> git
> >> a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c index
> >> 91023b9..8dbdffc 100644
> >> --- a/drivers/net/ixgbe/ixgbe_rxtx.c
> >> +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
> >> @@ -2085,11 +2085,19 @@ ixgbe_dev_tx_queue_setup(struct rte_eth_dev
> >> *dev,
> >>   	struct ixgbe_tx_queue *txq;
> >>   	struct ixgbe_hw     *hw;
> >>   	uint16_t tx_rs_thresh, tx_free_thresh;
> >> +	bool rs_deferring_allowed;
> >>
> >>   	PMD_INIT_FUNC_TRACE();
> >>   	hw = IXGBE_DEV_PRIVATE_TO_HW(dev->data->dev_private);
> >>
> >>   	/*
> >> +	 * According to 82599 and x540 specifications RS bit *must* be set on
> the
> >> +	 * last descriptor of *every* packet. Therefore we will not allow the
> >> +	 * tx_rs_thresh above 1 for all NICs newer than 82598.
> >> +	 */
> >> +	rs_deferring_allowed = (hw->mac.type <= ixgbe_mac_82598EB);
> >> +
> >> +	/*
> >>   	 * Validate number of transmit descriptors.
> >>   	 * It must not exceed hardware maximum, and must be multiple
> >>   	 * of IXGBE_ALIGN.
> >> @@ -2110,6 +2118,8 @@ ixgbe_dev_tx_queue_setup(struct rte_eth_dev
> *dev,
> >>   	 * to transmit a packet is greater than the number of free TX
> >>   	 * descriptors.
> >>   	 * The following constraints must be satisfied:
> >> +	 *  tx_rs_thresh must be less than 2 for NICs for which RS deferring is
> >> +	 *  forbidden (all but 82598).
> >>   	 *  tx_rs_thresh must be greater than 0.
> >>   	 *  tx_rs_thresh must be less than the size of the ring minus 2.
> >>   	 *  tx_rs_thresh must be less than or equal to tx_free_thresh.
> >> @@ -2121,9 +2131,20 @@ ixgbe_dev_tx_queue_setup(struct rte_eth_dev
> *dev,
> >>   	 * When set to zero use default values.
> >>   	 */
> >>   	tx_rs_thresh = (uint16_t)((tx_conf->tx_rs_thresh) ?
> >> -			tx_conf->tx_rs_thresh : DEFAULT_TX_RS_THRESH);
> >> +			tx_conf->tx_rs_thresh :
> >> +			(rs_deferring_allowed ? DEFAULT_TX_RS_THRESH : 1));
> >>   	tx_free_thresh = (uint16_t)((tx_conf->tx_free_thresh) ?
> >>   			tx_conf->tx_free_thresh : DEFAULT_TX_FREE_THRESH);
> >> +
> >> +	if (!rs_deferring_allowed && tx_rs_thresh > 1) {
> >> +		PMD_INIT_LOG(ERR, "tx_rs_thresh must be less than 2 since RS
> "
> >> +				  "must be set for every packet for this HW. "
> >> +				  "(tx_rs_thresh=%u port=%d queue=%d)",
> >> +			     (unsigned int)tx_rs_thresh,
> >> +			     (int)dev->data->port_id, (int)queue_idx);
> >> +		return -(EINVAL);
> >> +	}
> >> +
> >>   	if (tx_rs_thresh >= (nb_desc - 2)) {
> >>   		PMD_INIT_LOG(ERR, "tx_rs_thresh must be less than the
> number "
> >>   			     "of TX descriptors minus 2. (tx_rs_thresh=%u "
> >> --
> >> 2.1.0



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