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

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Message-ID: <YzXHxf/5WaiIrqMi@liuwe-devbox-debian-v2>
Date:   Thu, 29 Sep 2022 16:28:53 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>, 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,
        Wei Liu <wei.liu@...nel.org>
Subject: Re: [PATCH] drm/hyperv: Add ratelimit on error message

On Sun, Sep 11, 2022 at 09:11:42AM -0700, Saurabh Singh Sengar wrote:
> 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.

Applied to hyperv-next. Thanks.