Re: [PATCH 08/28] check-parallel: add logwrite device support

[Dave Chinner <david@fromorbit.com>]

On Wed, May 07, 2025 at 01:48:03PM +0530, Nirjhar Roy (IBM) wrote:
> On Thu, 2025-04-17 at 13:00 +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > Every logwrite test will use the same /dev/mapper/<dev>
> > name for the logwrites device, so we also need to convert
> > common/dmlogwrite to use per-test device names as we have done for
> > other dm devices.
> > 
> > Then add a per-test-runner LOGWRITES_DEV so that all tests using
> > dm-logwrites now get run by check-parallel.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
.....
> > diff --git a/common/dmlogwrites b/common/dmlogwrites
> > index a27e1966a..7c3ad95c9 100644
> > --- a/common/dmlogwrites
> > +++ b/common/dmlogwrites
> > @@ -4,6 +4,9 @@
> >  #
> >  # common functions for setting up and tearing down a dm log-writes device
> >  
> > +LOGWRITES_NAME=logwrites-$seq
> if 2 different runners are running tests with the same $seq, won't
> there be a conflict? For example runner-0 is running xfs/xyz and
> runner-1 is running generic/xyz ? 

Yes, it could happen, but it won't happen right now as there is no
overlap in test numbers using dmlogwrites between different test
directories.

I do need to solve this generically (i.e. for all the dm device
types) in the near future because I want to be able to run the same
test N times in parallel. e.g do flakey test profiling really
quickly over thousands of iterations by running 64 instances of the
test at the same time.

For this use case, the dm device name cannot rely on the test
name/sequence number at all, and so I'm going to have to come up
with a unique ID of some kind for this purpose. It may be as simple
as encoding the unique runner ID along with the test sequence number
into the device name - it's not a difficult issue to solve.

Hence I haven't spent much more thought on it than that, because
I've answered the two main questions that were relevant: "can
I solve it?" (yes) and "do I need to solve it now?" (no).

-Dave.
-- 
Dave Chinner
david@fromorbit.com