linux-kernel - Re: [PATCH] misc: kgdbts: Display progress of asynchronous tests

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Message-ID: <100d1ca3-fcc3-e77b-66c4-3cd4c657e31b@linaro.org>
Date:   Thu, 14 Dec 2017 16:11:39 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Jason Wessel <jason.wessel@...driver.com>
Cc:     kgdb-bugreport@...ts.sourceforge.net,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, patches@...aro.org
Subject: Re: [PATCH] misc: kgdbts: Display progress of asynchronous tests

On 14/12/17 15:20, Jason Wessel wrote:
> On 12/12/2017 06:10 AM, Daniel Thompson wrote:
>> kgdbts includes a couple of different "thrashing" style tests that
>> may have long runtimes (especially on simulated platforms) and which
>> run asynchronously. This is uncomfortable for interactive use and
>> makes setting timeouts tricky for automatic use.
> 
> 
> Do you know which test was specifically causing a problem?  It might not 
> be documented anywhere but I had usually started a user space process 
> which quickly created and deleted user space processes in order to make 
> the kgdbts tests complete quickly.

kgdbts=V1S10000 was bumping into 30 second timeouts.

IIRC this was simulating arm hardware on a fairly powerful x86 host 
machine. You can see the temporary workaround I used here:
https://github.com/daniel-thompson/kcontest/blob/master/tests/test_kgdb_selftest.py#L114

I decided this workaround was insufficient however since it would be 
rather brittle if I wanted to move to slower (more power efficient) 
hardware.

> I don't really see any issue with emitting a printk to indicate progress 
> as it is debug only and test specific.  As you know printk's change 
> timing.  If I had a dime for each time I had seen a problem go away when 
> I started adding printk's I'd have at least a 50 cents.  :-)

Agree about the interference.

I worked on the basis that these are thrashing style tests so providing 
there is a human perceivable gap between console messages (i.e. we are 
not "wasting" a CPU on an SMP system by having it in printk all the 
time) then perturbing the timing with printk() could even be beneficial.

Daniel.