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

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Date:   Sat, 12 Feb 2022 00:35:08 -0800
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Johannes Berg <johannes@...solutions.net>,
        Greg KH <gregkh@...uxfoundation.org>
CC:     <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

Hi Johannes

On 2/12/2022 12:24 AM, Johannes Berg wrote:
> On Fri, 2022-02-11 at 23:52 -0800, Abhinav Kumar wrote:
>>
>> 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.
>>
> 
> That seems kind of hard to believe, let's say it's a 4/3 split (4
> minutes reading, 3 minutes writing, to make read > write as you say),
> and 3MiB size, that'd mean you get 12.8KiB/sec? That seems implausibly
> low, unless you're reading with really tiny buffers?
> 
> Can you strace this somehow? (with timestamp info)
> 

Yes, like I have already mentioned in earlier comments, we continue to 
check whats taking that long.

Once we find something from our analysis and also have the trace, will 
update the thread.

>> Just doubling what we have currently. I am not sure how the current 5
>> mins timeout came from.
>>
> 
> To be honest it came out of thin air, and wasn't really meant as a limit
> on how fast you can read (feels like even if it's tens of MiB you should
> read it in milliseconds into userspace), but more of a maximum time that
> we're willing to waste kernel memory if nobody is around to read the
> data.
> 
> I thought it'd be better if we could somehow pin it while the userspace
> is reading it, but OTOH maybe that's actually bad, since that means
> userspace (though suitably privileged) could pin this kernel memory
> indefinitely.
> 
> johannes