linux-kernel - Re: [PATCH] drm/hyperv: Add ratelimit on error message

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Message-ID: <20220911161142.GA7754@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date:   Sun, 11 Sep 2022 09:11:42 -0700
From:   Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     ssengar@...rosoft.com, drawat.floss@...il.com, airlied@...ux.ie,
        daniel@...ll.ch, linux-hyperv@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        mikelley@...rosoft.com
Subject: Re: [PATCH] drm/hyperv: Add ratelimit on error message

On Sat, Sep 10, 2022 at 08:06:05PM +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 09.09.22 um 17:09 schrieb Saurabh Sengar:
> >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.
> >Rate limiting the error message, also output the error code for additional
> >diagnosability.
> >
> >Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> >---
> >  drivers/gpu/drm/hyperv/hyperv_drm_proto.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
> >index 76a182a..013a782 100644
> >--- a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
> >+++ b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
> >@@ -208,7 +208,7 @@ static inline int hyperv_sendpacket(struct hv_device *hdev, struct synthvid_msg
> >  			       VM_PKT_DATA_INBAND, 0);
> >  	if (ret)
> >-		drm_err(&hv->dev, "Unable to send packet via vmbus\n");
> >+		drm_err_ratelimited(&hv->dev, "Unable to send packet via vmbus; error %d\n", ret);
> 
> I better option would probably be drm_err_once(). Then you'd get the
> first error message and skip all others.

Thanks for your comment however the intention here is to limit the printk messages and break the chain
rather then printing only once. There can be cases where at different point of time we again get a
ring buffer full condition and we don't want to miss that. We should get the message for each of these
errror which are widely-separated in time not just the first time.

> 
> Best regards
> Thomas
> 
> >  	return ret;
> >  }
> 
> -- 
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Ivo Totev