Re: [dpdk-dev] [PATCH v7] eal: add manual probing option

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 23 Jan 2020 10:58:13 +0100
Gaetan Rivet <grive@u256.net> wrote:

> Add a new EAL option enabling manual probing in the EAL.
> This command line option will configure the EAL so that buses
> will not trigger their probe step on their own.
> 
> Applications are then expected to hotplug devices as they see fit.
> 
> Devices declared on the command line by the user (using -w and --vdev),
> will be probed using the hotplug API, in the order they are declared.
> 
> This has the effect of offering a way for users to control probe order
> of their devices, for drivers requiring it.
> 
> Signed-off-by: Gaetan Rivet <grive@u256.net>
> Acked-by : Vamsi Attunuru <vattunuru@marvell.com>
> Tested-by: Vamsi Attunuru <vattunuru@marvell.com>
> Reviewed-by: Jerin Jacob <jerinj@marvell.com>
> ---
> 
>  haven't heard many opinions on the matter, please shout if you see an issue
> with this approach.
> 
> @Slava: I have tested rather quickly that it does not break anything,
>         and that it works as intended for basic cases.
>         Can you test it further for your use-case and tell me if it works fine?
> 
> Beyond the obvious difference between both probe mode, something to keep in mind:
> while using -w on invalid devices would not block (PCI) bus probing, it will stop manual
> probing in its track. All devices need to exist and be valid device IDs.
> 
> v2: fixed a few typos, map file (and used Travis to validate).
> 
>     Slava, are you able to test this patch?
> 
> v3: properly fixed the map file (inherited 19.08 instead of 19.05).
> 
>     Added a function to set the probe manual from the application,
>     without having the user do it from the command line.
> 
>     Stopped spamming Slava about it, Vamsi was actually the one interested in it!
> 
> Standing issue worth chiming in:
> 
>   Currently manual-probe will cut off probing from all buses.
>   It could be interesting to be able to only cut buses supporting hotplug,
>   given that they are the one able to probe devices afterward.
> 
>   No real use-case for this right now, so leaving as-is. Might be worth
>   considering in the future.
> 
> v4: Rebased on master,
>     Moved implementation in common EAL,
>     Used public API within the EAL to set the option,
>     Made the API experimental
> 
> v5: added note in the Getting Started Guide.
> 
> v6: Rebased on master
> 
>     see http://mails.dpdk.org/archives/dev/2020-January/154178.html
>     for reference to this version, linking v7 to v5 thread.
> 
> v7: Updated author and SoB.
> 
>  doc/guides/linux_gsg/eal_args.include.rst  | 13 ++++++
>  doc/guides/rel_notes/release_20_02.rst     |  9 ++++
>  lib/librte_eal/common/eal_common_bus.c     |  6 +++
>  lib/librte_eal/common/eal_common_dev.c     | 54 ++++++++++++++++++++++
>  lib/librte_eal/common/eal_common_options.c |  8 ++++
>  lib/librte_eal/common/eal_internal_cfg.h   |  1 +
>  lib/librte_eal/common/eal_options.h        |  2 +
>  lib/librte_eal/common/eal_private.h        |  9 ++++
>  lib/librte_eal/common/include/rte_eal.h    | 36 +++++++++++++++
>  lib/librte_eal/rte_eal_version.map         |  4 ++
>  10 files changed, 142 insertions(+)

This patch seems to have been held in limbo for 3 years.

For me, it is ok, but concerned that it opens up a whole scenario of possible
usages that may not be tested, and probably don't work. Testing all the possible
combinations of probe ordering is a geometric problem.

So if user submits bug then the response would have to be:
  Manual probing is an experimental option which may not work.