linux-kernel - Re: [PATCH] habanalabs: print to kernel log when reset is finished

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Message-ID: <20190811073856.GC3034@kroah.com>
Date:   Sun, 11 Aug 2019 09:38:56 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Oded Gabbay <oded.gabbay@...il.com>
Cc:     "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        Omer Shpigelman <oshpigelman@...ana.ai>,
        Tomer Tayar <ttayar@...ana.ai>
Subject: Re: [PATCH] habanalabs: print to kernel log when reset is finished

On Sat, Aug 10, 2019 at 08:45:54PM +0300, Oded Gabbay wrote:
> On Sat, Aug 10, 2019 at 8:23 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Sat, Aug 10, 2019 at 06:29:16PM +0300, Oded Gabbay wrote:
> > > On Sat, Aug 10, 2019 at 3:53 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> > > >
> > > > On Sat, Aug 10, 2019 at 03:38:08PM +0300, Oded Gabbay wrote:
> > > > > Now that we don't print the queue testing messages, we need to print when
> > > > > the reset is finished so whoever looks at the kernel log will know the
> > > > > reset process was finished successfully and the driver is not stuck.
> > > > >
> > > > > Signed-off-by: Oded Gabbay <oded.gabbay@...il.com>
> > > > > ---
> > > > >  drivers/misc/habanalabs/device.c | 2 ++
> > > > >  1 file changed, 2 insertions(+)
> > > > >
> > > > > diff --git a/drivers/misc/habanalabs/device.c b/drivers/misc/habanalabs/device.c
> > > > > index 9a5926888b99..1fac808c2546 100644
> > > > > --- a/drivers/misc/habanalabs/device.c
> > > > > +++ b/drivers/misc/habanalabs/device.c
> > > > > @@ -907,6 +907,8 @@ int hl_device_reset(struct hl_device *hdev, bool hard_reset,
> > > > >       else
> > > > >               hdev->soft_reset_cnt++;
> > > > >
> > > > > +     dev_info(hdev->dev, "Successfully finished resetting the device\n");
> > > >
> > > > Really?  For doing things "properly" there is no need to spam the kernel
> > > > log.  Only spit stuff out if an error happens.
> > > >
> > > > thanks,
> > > >
> > > > greg k-h
> > >
> > > I beg to differ for two reasons:
> > > 1. Reset happens very rarely, if at all. So this message (that get
> > > printed after reset is done) will definitely not spam the kernel log.
> > > 2. When a reset starts we print an appropriate error message. I think
> > > it is expected by the user that we will also print if and when the
> > > reset has finished successfully. I really believe that lack of this
> > > printing might be deceiving for users.
> >
> > How is anyone going to parse the kernel log for anything to know if
> > something happens?
> 
> Actually our jenkins server parse the kernel log and look for bad
> messages from the driver...
> But the main reason for this, IMO, is for developers (in userspace)
> that run with a terminal open on the kernel log to see if something
> bad happens while they run their applications.
> 
> >
> > How do you trigger a reset?  Is it done by userspace?  If so, just
> > notify them then.
> 
> Reset can be triggered by two main reasons, but a userspace
> application is *not* one of them.
> It can be due to a command submission not finishing in time or from a
> major error in the device (e.g. double ECC error).
> That's why I think it is important to tell them the reset +
> re-initialization flow was finished successfully.
> Of course all this information, let's call it operational status, can
> be acquired by the INFO IOCTL the driver provides, but it is *really*
> convenient, IMHO, to see these type of messages in the kernel log
> while they happen.

Ah, yes, if this is something that userspace can not trigger then it's
ok.  But you should then make it a 'dev_warn' to match up with the
message level when the reset starts.

thanks,

greg k-h