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From: Matan Azrad <matan@nvidia.com>
To: Chengchang Tang <tangchengchang@huawei.com>,
	"dev@dpdk.org" <dev@dpdk.org>
Cc: "maryam.tahhan@intel.com" <maryam.tahhan@intel.com>,
	"linuxarm@huawei.com" <linuxarm@huawei.com>,
	"ferruh.yigit@intel.com" <ferruh.yigit@intel.com>,
	 "wenzhuo.lu@intel.com" <wenzhuo.lu@intel.com>,
	NBU-Contact-Thomas Monjalon <thomas@monjalon.net>,
	"arybchenko@solarflare.com" <arybchenko@solarflare.com>
Subject: Re: [dpdk-dev] [PATCH v3 1/4] ethdev: add a field for rxq info structure
Date: Sun, 6 Sep 2020 13:45:48 +0000
Message-ID: <MW2PR12MB24920794C311C12198F57794DF2B0@MW2PR12MB2492.namprd12.prod.outlook.com> (raw)
In-Reply-To: <a2cc0573-0149-0724-c3c8-86b48c0552d5@huawei.com>


Hi  Chengchang

From: Chengchang Tang:
> Hi, Matan
> 
> On 2020/9/2 18:30, Matan Azrad wrote:
> > Hi Chengchang
> >
> > From: Chengchang Tang
> >> Hi, Matan
> >>
> >> On 2020/9/2 15:19, Matan Azrad wrote:
> >>>
> >>> Hi Chengchang
> >>>
> >>> From: Chengchang Tang
> >>>> Hi, Matan
> >>>>
> >>>> On 2020/9/1 23:33, Matan Azrad wrote:
> >>>>>
> >>>>> Hi Chengchang
> >>>>>
> >>>>> Please see some question below.
> >>>>>
> >>>>> From: Chengchang Tang
> >>>>>> Add a field named rx_buf_size in rte_eth_rxq_info to indicate the
> >>>>>> buffer size used in receiving packets for HW.
> >>>>>>
> >>>>>> In this way, upper-layer users can get this information by
> >>>>>> calling rte_eth_rx_queue_info_get.
> >>>>>>
> >>>>>> Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
> >>>>>> Reviewed-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>
> >>>>>> Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
> >>>>>> ---
> >>>>>>  lib/librte_ethdev/rte_ethdev.h | 2 ++
> >>>>>>  1 file changed, 2 insertions(+)
> >>>>>>
> >>>>>> diff --git a/lib/librte_ethdev/rte_ethdev.h
> >>>>>> b/lib/librte_ethdev/rte_ethdev.h index 70295d7..9fed5cb 100644
> >>>>>> --- a/lib/librte_ethdev/rte_ethdev.h
> >>>>>> +++ b/lib/librte_ethdev/rte_ethdev.h
> >>>>>> @@ -1420,6 +1420,8 @@ struct rte_eth_rxq_info {
> >>>>>>         struct rte_eth_rxconf conf; /**< queue config parameters. */
> >>>>>>         uint8_t scattered_rx;       /**< scattered packets RX supported.
> */
> >>>>>>         uint16_t nb_desc;           /**< configured number of RXDs. */
> >>>>>> +       /**< buffer size used for hardware when receive packets. */
> >>>>>> +       uint16_t rx_buf_size;
> >>>>>
> >>>>> Is it the maximum supported Rx buffer by the HW?
> >>>>> If yes, maybe max_rx_buf_size is better name?
> >>>>
> >>>> No, it is the Rx buffer size currently used by HW.
> >
> >>> Doesn't it defined by the user? Using Rx queue mem-pool mbuf room
> size?
> >>>
> >>> And it may be different per Rx queue....
> >>
> >> Yes, it is defined by user using the Rx queue mem-pool mbuf room size.
> >> When different queues are bound to different mempools, different
> >> queues may have different value.
> >>>
> >>>> IMHO, the structure rte_eth_rxq_info and associated query API are
> >>>> mainly used to query HW configurations at runtime or after queue is
> >>>> configured/setup. Therefore, the content of this structure should
> >>>> be the current HW configuration.
> >>>
> >>> It looks me more like capabilities...
> >>> The one which define the current configuration is the user by the
> >> configuration APIs(after reading the capabilities).
> >>
> >> I prefer to consider the structure rte_eth_dev_info as the capabilities.
> >
> > Yes.
> >
> >> Because rxq_info and associated APIs are not available until the
> >> queue is configured. And the max rx_buf_size is already exists in
> dev_info.
> >>>
> >>> I don't think we have here all the current configurations, so what
> >>> is special
> >> in this one?
> >>
> >> I think the structure is used to store the queue-related
> >> configuration, especially the final HW configuration that may be
> >> different from user configuration and some configurations that are
> >> not mandatory for the user(PMDs will use a default configuration).
> >> Such as the scatterred_rx and rx_drop_en in rte_eth_rxconf, some PMDs
> >> will adjust it in some cases based on their HW constraints.
> >
> > Ok, this struct(struct rte_eth_rxq_info) is new for me.
> > Thanks for the explanation.
> >
> >> This configuration item meets the above criteria. The value range of
> >> rx_buf_size varies according to HW. Some HW may require 1k-alignment,
> >> while others may require several fixed values. So, the PMDs will
> >> configure it based on their HW constraints. This results in
> >> difference between the user configuration and the actual
> >> configuration and this value affects the memory usage and performance.
> >> I think there's a need for a way to expose that information.
> >
> > So the user can configure X and the driver will use Y!=X?
> 
> Yes, it depends on the HW. In the queue setup API, it just checks whether
> the input is greater than the required minimum value. But HW usually has
> requirements for alignment and so on.
> So when X does not meet these requirements, PMDs will calculate a new
> value Y that meets these requirements to configure the hardware (Y <= X, to
> ensure no memory overflow occurs).
> > Should the application validate its own configurations after setting them
> successfully?
> 
> It depends on their own needs. The application should not be forced to
> verify it to avoid affecting the ease of use of PMDs. For some applications,
> they don't care about this value.

I understand, 
It looks me like a bad ping-pong between app and PMD (for all the fields in the struct),
And we should avoid adding fields to this structure if we can.

What's about adding field in rte_eth_dev_info to expose the rx buffer alignment supported by the PMD?
Then, application has all the knowledge you want to expose before the configuration.

> >
> >>>
> >>>>> Maybe document that 0 means - no limitation by HW?
> >>>>
> >>>> Yes, there is no need to fill this filed for HW that has no restrictions on
> it.
> >>>> I'll add it in v4.
> >>>>
> >>>>> Must application read it in order to know if its datapath should
> >>>>> handle
> >>>> multi-segment buffers?
> >>>>
> >>>> I think it's more appropriate to use scattered_rx to determine if
> >>>> multi- segment buffers should be handled.
> >>>>
> >>>>>
> >>>>> Maybe it will be good to force application to configure scatter
> >>>>> when this
> >>>> field is valid and smaller than max_rx_pkt_len\max_lro.. (<= room
> size)...
> >>>
> >>> Can you explain more what is the issue you came to solve?
> >>
> >> This HW information may be useful when there is some problems running
> >> a application. This structure and related APIs can be used to expose
> >> it at run time.
> >>>
> > OK
> >
> > .
> >


  reply	other threads:[~2020-09-06 13:46 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-18 12:35 [dpdk-dev] [RFC] ethdev: add a field for rte_eth_rxq_info Chengchang Tang
2020-08-26  1:57 ` [dpdk-dev] [PATCH 0/3] add RX buffer size " Chengchang Tang
2020-08-26  1:57   ` [dpdk-dev] [PATCH 1/3] ethdev: add a field " Chengchang Tang
2020-08-26  1:57   ` [dpdk-dev] [PATCH 2/3] app/testpmd: Add RX buffer size display in queue info querry Chengchang Tang
2020-08-26  1:57   ` [dpdk-dev] [PATCH 3/3] net/hns3: add RX buffer size to rx qinfo querry Chengchang Tang
2020-08-26  7:12 ` [dpdk-dev] [PATCH v2 0/3] add Rx buffer size for rxq info structure Chengchang Tang
2020-08-26  7:12   ` [dpdk-dev] [PATCH v2 1/3] ethdev: add a field " Chengchang Tang
2020-08-26  7:29     ` Wei Hu (Xavier)
2020-08-26  7:12   ` [dpdk-dev] [PATCH v2 2/3] app/testpmd: add Rx buffer size display in queue info query Chengchang Tang
2020-08-26  7:28     ` Wei Hu (Xavier)
2020-08-26 14:42     ` Stephen Hemminger
2020-08-29  6:48       ` Chengchang Tang
2020-08-26  7:12   ` [dpdk-dev] [PATCH v2 3/3] net/hns3: add Rx buffer size to Rx qinfo query Chengchang Tang
2020-08-26  7:20     ` Wei Hu (Xavier)
2020-08-29  7:13 ` [dpdk-dev] [PATCH v3 0/4] add Rx buffer size for rxq info structure Chengchang Tang
2020-08-29  7:13   ` [dpdk-dev] [PATCH v3 1/4] ethdev: add a field " Chengchang Tang
2020-09-01 15:33     ` Matan Azrad
2020-09-02  3:52       ` Chengchang Tang
2020-09-02  7:19         ` Matan Azrad
2020-09-02 10:01           ` Chengchang Tang
2020-09-02 10:30             ` Matan Azrad
2020-09-03  1:48               ` Chengchang Tang
2020-09-06 13:45                 ` Matan Azrad [this message]
2020-09-07  7:47                   ` Chengchang Tang
2020-09-07  8:28                     ` Matan Azrad
2020-09-07 12:06                       ` Chengchang Tang
2020-09-07 13:02                         ` Matan Azrad
2020-09-03 15:00           ` Ferruh Yigit
2020-09-03 14:55         ` Ferruh Yigit
2020-09-03 15:01     ` Ferruh Yigit
2020-09-04  1:43       ` Chengchang Tang
2020-09-03 15:35     ` Bruce Richardson
2020-09-04 14:25       ` Ferruh Yigit
2020-09-04 15:14         ` Bruce Richardson
2020-09-04 15:30         ` Bruce Richardson
2020-08-29  7:13   ` [dpdk-dev] [PATCH v3 2/4] app/testpmd: add Rx buffer size display in queue info query Chengchang Tang
2020-08-29  7:13   ` [dpdk-dev] [PATCH v3 3/4] app/procinfo: add Rx buffer size to --show-port Chengchang Tang
2020-08-29  7:13   ` [dpdk-dev] [PATCH v3 4/4] net/hns3: add Rx buffer size to Rx qinfo query Chengchang Tang
2020-09-05  9:07 ` [dpdk-dev] [PATCH v4 0/5] add Rx buffer size for rxq info structure Chengchang Tang
2020-09-05  9:07   ` [dpdk-dev] [PATCH v4 1/5] ethdev: add a field " Chengchang Tang
2020-09-05 16:50     ` Stephen Hemminger
2020-09-05  9:07   ` [dpdk-dev] [PATCH v4 2/5] app/testpmd: add Rx buffer size display in queue info query Chengchang Tang
2020-09-18  8:54     ` Ferruh Yigit
2020-09-20  8:47       ` Chengchang Tang
2020-09-05  9:07   ` [dpdk-dev] [PATCH v4 3/5] app/procinfo: add Rx buffer size to --show-port Chengchang Tang
2020-09-05 16:59     ` Stephen Hemminger
2020-09-07  9:14       ` Chengchang Tang
2020-09-18 22:11         ` Stephen Hemminger
2020-09-21  2:06           ` Chengchang Tang
2020-09-21 11:26             ` Ferruh Yigit
2020-09-05  9:07   ` [dpdk-dev] [PATCH v4 4/5] net/hns3: add Rx buffer size to Rx qinfo query Chengchang Tang
2020-09-05  9:07   ` [dpdk-dev] [PATCH v4 5/5] doc: remove rxq info structure deprecation notice Chengchang Tang
2020-09-05 16:33     ` Thomas Monjalon
2020-09-07  9:12       ` Chengchang Tang
2020-09-21 13:22 ` [dpdk-dev] [PATCH v5 0/2] add Rx buffer size for rxq info structure Chengchang Tang
2020-09-21 13:22   ` [dpdk-dev] [PATCH v5 1/2] ethdev: add a field " Chengchang Tang
2020-09-21 14:18     ` Ferruh Yigit
2020-09-21 13:22   ` [dpdk-dev] [PATCH v5 2/2] net/hns3: add Rx buffer size to Rx qinfo query Chengchang Tang
2020-09-21 14:19   ` [dpdk-dev] [PATCH v5 0/2] add Rx buffer size for rxq info structure Ferruh Yigit

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