linux-kernel - Re: [PATCH] devcoredump: increase the device delete timeout to 10 mins

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Date:   Sat, 12 Feb 2022 08:04:11 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     johannes@...solutions.net, linux-kernel@...r.kernel.org,
        rafael@...nel.org, robdclark@...il.com,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, seanpaul@...omium.org,
        swboyd@...omium.org, nganji@...eaurora.org,
        aravindh@...eaurora.org, khsieh@...eaurora.org, daniel@...ll.ch,
        dmitry.baryshkov@...aro.org
Subject: Re: [PATCH] devcoredump: increase the device delete timeout to 10
 mins

On Fri, Feb 11, 2022 at 10:59:39AM -0800, Abhinav Kumar wrote:
> Hi Greg
> 
> Thanks for the response.
> 
> On 2/11/2022 3:09 AM, Greg KH wrote:
> > On Tue, Feb 08, 2022 at 11:44:32AM -0800, Abhinav Kumar wrote:
> > > There are cases where depending on the size of the devcoredump and the speed
> > > at which the usermode reads the dump, it can take longer than the current 5 mins
> > > timeout.
> > > 
> > > This can lead to incomplete dumps as the device is deleted once the timeout expires.
> > > 
> > > One example is below where it took 6 mins for the devcoredump to be completely read.
> > > 
> > > 04:22:24.668 23916 23994 I HWDeviceDRM::DumpDebugData: Opening /sys/class/devcoredump/devcd6/data
> > > 04:28:35.377 23916 23994 W HWDeviceDRM::DumpDebugData: Freeing devcoredump node
> > 
> > What makes this so slow?  Reading from the kernel shouldn't be the
> > limit, is it where the data is being sent to?
> 
> We are still checking this. We are seeing better read times when we bump up
> the thread priority of the thread which was reading this.

Where is the thread sending the data to?

> We are also trying to check if bumping up CPU speed is helping.
> But, results have not been consistently good enough. So we thought we should
> also increase the timeout to be safe.

Why would 10 minutes be better than 30?  What should the limit be?  :)

thanks,

greg k-h