From: Olivier Matz <olivier.matz@6wind.com>
To: "Zhao1, Wei" <wei.zhao1@intel.com>
Cc: "Zhang, Qi Z" <qi.z.zhang@intel.com>,
"dev@dpdk.org" <dev@dpdk.org>,
"Lu, Wenzhuo" <wenzhuo.lu@intel.com>
Subject: Re: [dpdk-dev] [RFC] net/ixgbe: fix Tx descriptor status api
Date: Tue, 26 Jun 2018 10:46:08 +0200 [thread overview]
Message-ID: <20180626084608.c4kfsc5ccnfwypgw@platinum> (raw)
In-Reply-To: <A2573D2ACFCADC41BB3BE09C6DE313CA07DFF21F@PGSMSX103.gar.corp.intel.com>
Hi Wei,
On Tue, Jun 26, 2018 at 01:38:22AM +0000, Zhao1, Wei wrote:
> Hi, Olivier Matz
>
> Will you commit fix patch for i40e and ixgbe and em?
If you think the patch are relevant, yes :)
Here is a pre-version (last 5 patches):
http://git.droids-corp.org/?p=dpdk.git;a=shortlog;h=refs/heads/tx-desc
It still need to fix checkpatch issues, few more tests, and
rebase on next-net.
> And the code " dd = (desc / txq->tx_rs_thresh + 1) * txq->tx_rs_thresh - 1;"
> Is only proper for tx function ixgbe_xmit_pkts_simple and ixgbe_xmit_pkts_vec ().
> But not proper for ixgbe_xmit_pkts (), the RS bit set rule is different from all these two.
Can you please give more detail please?
Note this code, maybe you are talking about this?
+ /* In full featured mode, RS bit is only set in the last descriptor */
+ /* of a multisegments packet */
+ if (!((txq->offloads == 0) &&
+ (txq->tx_rs_thresh >= RTE_PMD_IXGBE_TX_MAX_BURST)))
+ dd = txq->sw_ring[dd].last_id;
Maybe there is something better to test?
Just to ensure we are on the same line, here are some more infos.
===
- sw advances the tail pointer
- hw advances the head pointer
- the software populates the ring with full buffers to be sent by
the hw
- head points to the in-progress descriptor.
- sw writes new descriptors at tail
- head == tail means that the transmit queue is empty
- when the hw has processed a descriptor, it sets the DD bit if
the descriptor has the RS (report status) bit.
- the driver never reads the head (needs a pci transaction), instead
it monitors the DD bit of a descriptor that has the RS bit
txq->tx_tail: sw value for tail register
txq->tx_free_thresh: free buffers if count(free descs) < this value
txq->tx_rs_thresh: RS bit is set every rs_thresh descriptor
txq->tx_next_dd: next desc to scan for DD bit
txq->tx_next_rs: next desc to set RS bit
txq->last_desc_cleaned: last descriptor that have been cleaned
txq->nb_tx_free: number of free descriptors
Example:
|----------------------------------------------------------------|
| D R R R |
| ............xxxxxxxxxxxxxxxxxxxxxxxxx |
| <descs sent><- descs not sent yet -> |
| ............xxxxxxxxxxxxxxxxxxxxxxxxx |
|----------------------------------------------------------------|
^last_desc_cleaned=8 ^next_rs=47
^next_dd=15 ^sw_tail=45
^hw_head=20
<---- nb_used --------->
The hardware is currently processing the descriptor 20
'R' means the descriptor has the RS bit
'D' means the descriptor has the DD + RS bits
'x' are packets in txq (not sent)
'.' are packet already sent but not freed by sw
In this example, we have rs_thres=8. On next call to
ixgbe_tx_free_bufs(), some buffers will be freed.
===
Let's call ixgbe_dev_tx_descriptor_status(10):
- original version:
desc = 45 + 10 = 55
desc = ((55 + 8 - 1) / 8) * 8 = (62 / 8) * 8 = 56
wrong because it goes in the wrong direction, and because
56 does not have the RS bit
- after your patch:
desc = 45 + 10 = 55
desc = (((55 / 8) + 1) * 8) - 1 = (7 * 8) - 1 = 55
wrong because it goes in the wrong direction
- after my patch
desc = 45 - 10 - 1 = 34
desc = (((34 / 8) + 1) * 8) - 1 = (5 * 8) - 1 = 39
looks correct
Regards,
Olivier
next prev parent reply other threads:[~2018-06-26 8:46 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-22 8:38 [dpdk-dev] [PATCH] net/ixgbe: fix Tx check descriptor status APIs error Wei Zhao
2018-06-22 13:47 ` Zhang, Qi Z
2018-06-25 1:57 ` Zhao1, Wei
2018-06-25 2:48 ` Zhang, Qi Z
2018-06-25 5:58 ` Zhao1, Wei
2018-06-25 6:49 ` Zhao1, Wei
2018-06-25 7:47 ` Zhang, Qi Z
2018-06-25 7:52 ` Zhao1, Wei
2018-06-25 7:55 ` Zhang, Qi Z
2018-06-25 8:41 ` Zhao1, Wei
2018-06-25 14:20 ` [dpdk-dev] [RFC] net/ixgbe: fix Tx descriptor status api Olivier Matz
2018-06-25 14:30 ` Olivier Matz
2018-06-26 1:38 ` Zhao1, Wei
2018-06-26 8:46 ` Olivier Matz [this message]
2018-06-27 2:07 ` Zhao1, Wei
2018-06-27 13:38 ` Zhang, Qi Z
2018-06-26 1:24 ` [dpdk-dev] [PATCH v2] net/ixgbe: fix Tx check descriptor status APIs error Wei Zhao
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