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Message-ID: <b9156bde-137c-2fac-19e0-b205ab4d6016@quicinc.com>
Date:   Fri, 11 Feb 2022 23:52:41 -0800
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Subject: Re: [PATCH] devcoredump: increase the device delete timeout to 10
 mins
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To:     Greg KH <gregkh@linuxfoundation.org>
CC:     <johannes@sipsolutions.net>, <linux-kernel@vger.kernel.org>,
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References: <1644349472-31077-1-git-send-email-quic_abhinavk@quicinc.com>
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From:   Abhinav Kumar <quic_abhinavk@quicinc.com>
In-Reply-To: <Ygdb63FrorUsX/Hg@kroah.com>
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Hi Greg

On 2/11/2022 11:04 PM, Greg KH wrote:
> 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?

The thread is writing the data to a file in local storage. From our 
profiling, the read is the one taking the time not the write.

> 
>> 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?  :)

Again, this is from our profiling. We are seeing a worst case time of 7 
mins to finish the read for our data. Thats where the 10mins came from. 
Just doubling what we have currently. I am not sure how the current 5 
mins timeout came from.

> 
> thanks,
> 
> greg k-h