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From:   Rob Clark <robdclark@gmail.com>
Date:   Tue, 1 Mar 2022 09:45:39 -0800
Message-ID: <CAF6AEGtNGJanJ9f2pkjst50yPSWGJPo5nDkcZZgq=BkRWMq4yg@mail.gmail.com>
Subject: Re: [PATCH] devcoredump: increase the device delete timeout to 10 mins
To:     David Laight <David.Laight@aculab.com>
Cc:     Abhinav Kumar <quic_abhinavk@quicinc.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        Greg KH <gregkh@linuxfoundation.org>,
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On Mon, Feb 28, 2022 at 10:49 PM David Laight <David.Laight@aculab.com> wrote:
>
> From: Abhinav Kumar
> > Sent: 28 February 2022 21:38
> ...
> > We also did some profiling around how much increasing the block size
> > helps and here is the data:
> >
> > Block size    cost
> >
> > 4KB           229s
> > 8KB            86s
>
> You must have an O(n^2) operation in there - find it.

The problem is how the devcoredump/sysfs interface works, which
results in "re-rendering" the output for each block.. it's fine for
moderate size sysfs files, but scales quite badly once you get into
couple MB size sysfs files.

It could be fixed by having some way to keep state across successive
read callbacks.

BR,
-R

>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)