Subject: Re: [PATCH 11/15] RDMA/hbl: add habanalabs RDMA driver

From: Leon Romanovsky <[email-masked]>
Date: Tue, 18 Jun 2024 15:58:42 +0300

On Tue, Jun 18, 2024 at 11:08:34AM +0000, Omer Shpigelman wrote:
> On 6/17/24 22:04, Leon Romanovsky wrote:
> > [Some people who received this message don't often get email from [email-masked]. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> > 
> > On Mon, Jun 17, 2024 at 05:43:49PM +0000, Omer Shpigelman wrote:
> >> On 6/13/24 22:18, Leon Romanovsky wrote:
> >>> [Some people who received this message don't often get email from [email-masked]. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> >>>
> >>> On Thu, Jun 13, 2024 at 11:22:04AM +0300, Omer Shpigelman wrote:
> >>>> Add an RDMA driver of Gaudi ASICs family for AI scaling.
> >>>> The driver itself is agnostic to the ASIC in action, it operates according
> >>>> to the capabilities that were passed on device initialization.
> >>>> The device is initialized by the hbl_cn driver via auxiliary bus.
> >>>> The driver also supports QP resource tracking and port/device HW counters.
> >>>>
> >>>> Signed-off-by: Omer Shpigelman <[email-masked]>
> >>>> Co-developed-by: Abhilash K V <[email-masked]>
> >>>> Signed-off-by: Abhilash K V <[email-masked]>
> >>>> Co-developed-by: Andrey Agranovich <[email-masked]>
> >>>> Signed-off-by: Andrey Agranovich <[email-masked]>
> >>>> Co-developed-by: Bharat Jauhari <[email-masked]>
> >>>> Signed-off-by: Bharat Jauhari <[email-masked]>
> >>>> Co-developed-by: David Meriin <[email-masked]>
> >>>> Signed-off-by: David Meriin <[email-masked]>
> >>>> Co-developed-by: Sagiv Ozeri <[email-masked]>
> >>>> Signed-off-by: Sagiv Ozeri <[email-masked]>
> >>>> Co-developed-by: Zvika Yehudai <[email-masked]>
> >>>> Signed-off-by: Zvika Yehudai <[email-masked]>
> >>>
> >>> I afraid that you misinterpreted the "Co-developed-by" tag. All these
> >>> people are probably touch the code and not actually sit together at
> >>> the same room and write the code together. So, please remove the
> >>> extensive "Co-developed-by" tags.
> >>>
> >>> It is not full review yet, but simple pass-by-comments.
> >>>
> >>
> >> Actually except of two, all of the mentioned persons sat in the same room
> >> and developed the code together.
> >> The remaining two are located on a different site (but also together).
> >> Isn't that what "Co-developed-by" tag for?
> >> I wanted to give them credit for writing the code but I can remove if it's
> >> not common.
> > 
> > Signed-off-by will be enough to give them credit.
> > 
> 
> Ok, good enough.
> 
> >>
> >>>> ---
> >>>>  MAINTAINERS                              |   10 +
> >>>>  drivers/infiniband/Kconfig               |    1 +
> >>>>  drivers/infiniband/hw/Makefile           |    1 +
> >>>>  drivers/infiniband/hw/hbl/Kconfig        |   17 +
> >>>>  drivers/infiniband/hw/hbl/Makefile       |    8 +
> >>>>  drivers/infiniband/hw/hbl/hbl.h          |  326 +++
> >>>>  drivers/infiniband/hw/hbl/hbl_main.c     |  478 ++++
> >>>>  drivers/infiniband/hw/hbl/hbl_verbs.c    | 2686 ++++++++++++++++++++++
> >>>>  include/uapi/rdma/hbl-abi.h              |  204 ++
> >>>>  include/uapi/rdma/hbl_user_ioctl_cmds.h  |   66 +
> >>>>  include/uapi/rdma/hbl_user_ioctl_verbs.h |  106 +
> >>>>  include/uapi/rdma/ib_user_ioctl_verbs.h  |    1 +
> >>>>  12 files changed, 3904 insertions(+)
> >>>>  create mode 100644 drivers/infiniband/hw/hbl/Kconfig
> >>>>  create mode 100644 drivers/infiniband/hw/hbl/Makefile
> >>>>  create mode 100644 drivers/infiniband/hw/hbl/hbl.h
> >>>>  create mode 100644 drivers/infiniband/hw/hbl/hbl_main.c
> >>>>  create mode 100644 drivers/infiniband/hw/hbl/hbl_verbs.c
> >>>>  create mode 100644 include/uapi/rdma/hbl-abi.h
> >>>>  create mode 100644 include/uapi/rdma/hbl_user_ioctl_cmds.h
> >>>>  create mode 100644 include/uapi/rdma/hbl_user_ioctl_verbs.h
> >>>
> >>> <...>
> >>>
> >>>> +#define hbl_ibdev_emerg(ibdev, format, ...)  ibdev_emerg(ibdev, format, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_alert(ibdev, format, ...)  ibdev_alert(ibdev, format, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_crit(ibdev, format, ...)   ibdev_crit(ibdev, format, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_err(ibdev, format, ...)    ibdev_err(ibdev, format, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_warn(ibdev, format, ...)   ibdev_warn(ibdev, format, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_notice(ibdev, format, ...) ibdev_notice(ibdev, format, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_info(ibdev, format, ...)   ibdev_info(ibdev, format, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_dbg(ibdev, format, ...)    ibdev_dbg(ibdev, format, ##__VA_ARGS__)
> >>>> +
> >>>> +#define hbl_ibdev_emerg_ratelimited(ibdev, fmt, ...)         \
> >>>> +     ibdev_emerg_ratelimited(ibdev, fmt, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_alert_ratelimited(ibdev, fmt, ...)         \
> >>>> +     ibdev_alert_ratelimited(ibdev, fmt, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_crit_ratelimited(ibdev, fmt, ...)          \
> >>>> +     ibdev_crit_ratelimited(ibdev, fmt, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_err_ratelimited(ibdev, fmt, ...)           \
> >>>> +     ibdev_err_ratelimited(ibdev, fmt, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_warn_ratelimited(ibdev, fmt, ...)          \
> >>>> +     ibdev_warn_ratelimited(ibdev, fmt, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_notice_ratelimited(ibdev, fmt, ...)                \
> >>>> +     ibdev_notice_ratelimited(ibdev, fmt, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_info_ratelimited(ibdev, fmt, ...)          \
> >>>> +     ibdev_info_ratelimited(ibdev, fmt, ##__VA_ARGS__)
> >>>> +#define hbl_ibdev_dbg_ratelimited(ibdev, fmt, ...)           \
> >>>> +     ibdev_dbg_ratelimited(ibdev, fmt, ##__VA_ARGS__)
> >>>> +
> >>>
> >>> Please don't redefine the existing macros. Just use the existing ones.
> >>>
> >>>
> >>> <...>
> >>>
> >>
> >> That's a leftover from some debug code. I'll remove.
> >>
> >>>> +     if (hbl_ib_match_netdev(ibdev, netdev))
> >>>> +             ib_port = hbl_to_ib_port_num(hdev, netdev->dev_port);
> >>>> +     else
> >>>> +             return NOTIFY_DONE;
> >>>
> >>> It is not kernel coding style. Please write:
> >>> if (!hbl_ib_match_netdev(ibdev, netdev))
> >>>     return NOTIFY_DONE;
> >>>
> >>> ib_port = hbl_to_ib_port_num(hdev, netdev->dev_port);
> >>>
> >>
> >> I'll fix the code, thanks.
> >>
> >>>> +
> >>>
> >>> <...>
> >>>
> >>>> +static int hbl_ib_probe(struct auxiliary_device *adev, const struct auxiliary_device_id *id)
> >>>> +{
> >>>> +     struct hbl_aux_dev *aux_dev = container_of(adev, struct hbl_aux_dev, adev);
> >>>> +     struct hbl_ib_aux_ops *aux_ops = aux_dev->aux_ops;
> >>>> +     struct hbl_ib_device *hdev;
> >>>> +     ktime_t timeout;
> >>>> +     int rc;
> >>>> +
> >>>> +     rc = hdev_init(aux_dev);
> >>>> +     if (rc) {
> >>>> +             dev_err(&aux_dev->adev.dev, "Failed to init hdev\n");
> >>>> +             return -EIO;
> >>>> +     }
> >>>> +
> >>>> +     hdev = aux_dev->priv;
> >>>> +
> >>>> +     /* don't allow module unloading while it is attached */
> >>>> +     if (!try_module_get(THIS_MODULE)) {
> >>>
> >>> This part makes wonder, what are you trying to do here? What doesn't work for you
> >>> in standard driver core and module load mechanism?
> >>>
> >>
> >> Before auxiliary bus was introduced, we used EXPORT_SYMBOLs for inter
> >> driver communication. That incremented the refcount of the used module so
> >> it couldn't be removed while it is in use.
> >> Auxiliary bus usage doesn't increment the used module refcount and hence
> >> the used module can be removed while it is in use and that's something
> >> we don't want to allow.
> >> We could solve it by some global locking or in_use atomic but the most
> >> simple and clean way is just to increment the used module refcount on
> >> auxiliary device probe and decrement it on auxiliary device removal.
> > 
> > No, you was supposed to continue to use EXPORT_SYMBOLs and don't
> > invent auxiliary ops structure (this is why you lost module
> > reference counting).
> > 
> 
> Sorry, but according to the auxiliary bus doc, a domain-specific ops
> structure can be used.
> We followed the usage example described at drivers/base/auxiliary.c.
> What am I missing? 

Being the one who implemented auxiliary bus in the kernel and converted
number of drivers to use it, I strongly recommend do NOT follow the example
provided there.

So you are missing "best practice", and "best practice" is to use
EXPORT_SYMBOLs and rely on module reference counting.

> Moreover, we'd like to support the mode where the IB or the ETH driver is
> not loaded at all. But this cannot be achieved if we use EXPORT_SYMBOLs
> exclusively for inter driver communication.

It is not true and not how the kernel works. You can perfectly load core
driver without IB and ETH, at some extent this is how mlx5 driver works.

> 
> >>
> >>>> +             dev_err(hdev->dev, "Failed to increment %s module refcount\n",
> >>>> +                     module_name(THIS_MODULE));
> >>>> +             rc = -EIO;
> >>>> +             goto module_get_err;
> >>>> +     }
> >>>> +
> >>>> +     timeout = ktime_add_ms(ktime_get(), hdev->pending_reset_long_timeout * MSEC_PER_SEC);
> >>>> +     while (1) {
> >>>> +             aux_ops->hw_access_lock(aux_dev);
> >>>> +
> >>>> +             /* if the device is operational, proceed to actual init while holding the lock in
> >>>> +              * order to prevent concurrent hard reset
> >>>> +              */
> >>>> +             if (aux_ops->device_operational(aux_dev))
> >>>> +                     break;
> >>>> +
> >>>> +             aux_ops->hw_access_unlock(aux_dev);
> >>>> +
> >>>> +             if (ktime_compare(ktime_get(), timeout) > 0) {
> >>>> +                     dev_err(hdev->dev, "Timeout while waiting for hard reset to finish\n");
> >>>> +                     rc = -EBUSY;
> >>>> +                     goto timeout_err;
> >>>> +             }
> >>>> +
> >>>> +             dev_notice_once(hdev->dev, "Waiting for hard reset to finish before probing IB\n");
> >>>> +
> >>>> +             msleep_interruptible(MSEC_PER_SEC);
> >>>> +     }
> >>>
> >>> The code above is unexpected.
> >>>
> >>
> >> We have no control on when the user insmod the IB driver.
> > 
> > It is not true, this is controlled through module dependencies
> > mechanism.
> > 
> 
> Yeah, if we would use EXPORT_SYMBOLs for inter driver communication but
> we don't.

So please use it and don't add complexity where it is not needed.

> 
> >> As a result it is possible that the IB auxiliary device will be probed
> >> while the compute device is under reset (due to some HW error).
> > 
> > No, it is not possible. If you structure your driver right.
> > 
> 
> Again, it is not possible if we would use EXPORT_SYMBOLs.
> Please let me know if we misunderstood something because AFAIU we followed
> the auxiliary bus doc usage example.

It is better to follow actual drivers that use auxiliary bus and see how
they implemented it and not rely on examples in the documentation.

Thanks

> > Thanks