Re: [PATCH 1/1] video: hyperv_fb: Add ratelimit on error message

From: Joe Perches <joe@perches.com>
To: Michael Kelley <mikelley@microsoft.com>,
	kys@microsoft.com, haiyangz@microsoft.com,
	sthemmin@microsoft.com, wei.liu@kernel.org,
	linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org,
	linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 1/1] video: hyperv_fb: Add ratelimit on error message
Date: Tue, 20 Apr 2021 12:58:48 -0700	[thread overview]
Message-ID: <c5de33a3cd1dc18688fc2bb7cf6a84aedcc5a041.camel@perches.com> (raw)
In-Reply-To: <1618933459-10585-1-git-send-email-mikelley@microsoft.com>

On Tue, 2021-04-20 at 08:44 -0700, Michael Kelley wrote:
> Due to a full ring buffer, the driver may be unable to send updates to
> the Hyper-V host.  But outputing the error message can make the problem
> worse because console output is also typically written to the frame
> buffer.  As a result, in some circumstances the error message is output
> continuously.
> 
> Break the cycle by rate limiting the error message.  Also output
> the error code for additional diagnosability.
> 
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>

None of the callers of this function ever check the return status.
Why is important/useful to emit this message at all?

> ---
>  drivers/video/fbdev/hyperv_fb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> index 4dc9077..a7e6eea 100644
> --- a/drivers/video/fbdev/hyperv_fb.c
> +++ b/drivers/video/fbdev/hyperv_fb.c
> @@ -308,7 +308,7 @@ static inline int synthvid_send(struct hv_device *hdev,
>  			       VM_PKT_DATA_INBAND, 0);
>  
> 
>  	if (ret)
> -		pr_err("Unable to send packet via vmbus\n");
> +		pr_err_ratelimited("Unable to send packet via vmbus; error %d\n", ret);
>  
> 
>  	return ret;
>  }