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Re: [Gnu-arch-users] GCC v. Arch address@hidden: Regressions on mainline

From: Jan Hudec
Subject: Re: [Gnu-arch-users] GCC v. Arch address@hidden: Regressions on mainline]
Date: Wed, 23 Jun 2004 09:38:28 +0200
User-agent: Mutt/1.5.6+20040523i

On Tue, Jun 22, 2004 at 22:21:34 -0700, Tom Lord wrote:
>     > From: Colin Walters <address@hidden>
>     > On Tue, 2004-06-22 at 19:15 -0700, Tom Lord wrote:
>     > > GCC commits happen too fast (last I checked) to serialize them while
>     > > inserting tests between each one.
>     > > I.e., just naively dropping a "make test" call into your PQM just
>     > > before the "tla commit" --- probably the commit queue will grow
>     > > without bound (until the developers notice and say, hey, this isn't
>     > > working :-).
>     > How else would you do it?  You could run the tests in parallel, which
>     > would scale up faster with more CPUs, but if you want to enforce the
>     > invariant that the test suite passes for every commit on the mainline -
>     > you have to run the test suite for every commit.
> So, to sum up...... if you want a process that says:
>         while (pending patch)
>         if (test is ok)
>              commit
> then your patch queue is rate limited by the greater of the commit
> time and the test time.   Test time for GCC will strongly dominate.
> Speeding up test times, through any combination of parallel builds,
> cached build results, precompiled headers etc --- are therefore,
> indeed, useful ways to raise the maximum commit rate of the above
> loop.
> But there's an upper bound on that commit rate and, for now anyway,
> I'm just pretending we know that the maximum commit rate for that loop
> is too low.
> That's not a bad thing to pretend.  _Absent_ compilation and
> test-execution speed-ups, the test rate is already too high to keep up
> with GCC commits.  [To be clear:  that's my rough recollection, not a
> proven result that I'm claiming.   It's my envelope calculation, not a
> proven fact.]
> Are the compilation and test-execution speed-ups viable?   In the long
> run as testing procedures get more complex?   I doubt it.   Remember
> that, ideally, these tests are repeated on several platforms.
> Nevermind that they can be done in parallel -- just pushing around the
> bits is already going to get you in trouble.

1) The current gcc approach, as I understood it, is, that before commit,
   each developer runs a test. If it then breaks because someone else
   commited a conflicting patch, it is resolved ex-post. So without the
   tests, arch-pqm would perform exactly as cvs does now.
2) A star of patch-queues. Since pqm can do star-merge, it would be
   possible to have several testing pqm-based branches. Merge requests
   first go there, are tested, and if they work, get merged into the
   mainline and tested as a bunch. The individual testing queues should
   be probably grouped by subsytems or features to be most useful.

                                                 Jan 'Bulb' Hudec 

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