Re: [PATCH] ethdev: add dump regs for telemetry

[Thomas Monjalon <thomas@monjalon.net>]

10/01/2024 13:15, Ferruh Yigit:
> On 1/10/2024 1:38 AM, fengchengwen wrote:
> > Hi Ferruh,
> > 
> > On 2024/1/10 2:06, Ferruh Yigit wrote:
> >> On 1/9/2024 2:19 AM, Jie Hai wrote:
> >>> On 2023/12/14 20:49, Ferruh Yigit wrote:
> >>>> On 12/14/2023 1:56 AM, Jie Hai wrote:
> >>>>> The ethdev library now registers a telemetry command for
> >>>>> dump regs.
> >>>>>
> >>>>> An example usage is shown below:
> >>>>> --> /ethdev/regs,test
> >>>>> {
> >>>>>    "/ethdev/regs": {
> >>>>>      "regs_offset": 0,
> >>>>>      "regs_length": 3192,
> >>>>>      "regs_width": 4,
> >>>>>      "device_version": "0x1080f00",
> >>>>>      "regs_file": "port_0_regs_test"
> >>>>>    }
> >>>>> }
> >>>
> >>>>
> >>>> Above code writes register data to a file.
> >>>>
> >>>> I am not sure about this kind of usage of telemetry command, that it
> >>>> cause data to be written to a file.
> >>>>
> >>>> My understanding is, telemetry usage is based on what telemetry client
> >>>> receives.
> >>>> What do you think just keep the 'reg_info' fields excluding data to the
> >>>> file?
> >>>>
> >>>> .Hi, Ferruh
> >>>
> >>> I tried to write all register information to telemetry data,
> >>> but gave up because some drivers had too many registers (eg.ixgbe)
> >>> to carry. Therefore, the writing data to file approach is selected.
> >>>
> >>> When we query a register, the register content is the key.
> >>> The information such as the width and length is only auxiliary
> >>> information. If the register data cannot be obtained, the auxiliary
> >>> information is optional. So I don't think register data should be removed.
> >>>
> >>> In my opinion, writing a file is a more appropriate way to do it.
> >>> I wonder if there's a better way.
> >>>
> >>>
> >>
> >> Is there a usecase to get register information from telemetry interface?
> > 
> > Among the available tools:
> > 1, ethtool/proc-info: should use multi-process mechanism to connect to the main process
> > 2, telemetry: easier, lighter load, and it don't need re-probe the ethdev in the secondary process,
> >               and also cost more resource, like hugepage, cores.
> > 
> > From our users, they prefer use the second 'telemetry', so I think we should move
> > more status-query-points to telemetry.
> > 
> > As for this question, I think it's okay to get register info from telemetry.
> > 
> > 
> >
> > Another question, we have some internal registers, which:
> > 1. Is not suitable expose by xstats, because they may includes configuration
> > 2. Is not suitable expose by dumps, because this dumps is hard to understand (because it only has value).
> > 
> > So we plan to add some telemetry points in the driver itself, so we could display them like xstats:
> > "xxxx" : 0x1234
> > "yyyy" : 0x100
> > 
> > Will the community accept this kind of telemetry points which limit one driver ?
> > 
> 
> Hi Chengwen,
> 
> I see there is a usecase/requirement.
> 
> With this patch, even using file, only register values are dumped and
> isn't it hard to find value of specific register?
> 
> ("xxxx" : 0x1234) approach looks better, but instead of making this
> telemetry support for specific driver, what about making it in two steps.
> 
> First add new dev_ops, (or update existing one), to get registers with
> "name: value" format, (in a way to allow empty name), or even perhaps
> "name: offset, value" format.

I'm OK to add an API for dumping registers, and guess what?
We already have it: rte_eth_dev_get_reg_info().
We may extend it to query a subset of registers.

> And in second stage add telemetry support around it.
> (Name being optional lets us wrap exiting 'get_reg' dev_ops with new one)

I am against overloading telemetry for debug purpose.

> When adding dev_ops, it may get an additional 'filter' parameter, to get
> only subset of regs, like "mac*" to get regs name staring with "mac",
> this may help for the cases there are too many registers you mentioned.
> 
> Anyway, we can discuss more about its design, but what do you think
> about first having a dev_ops for this?