GNU bug report logs - #24516

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From: Jim Meyering <jim <at> meyering.net>
To: "Nelson H. F. Beebe" <beebe <at> math.utah.edu>
Cc: 24516 <at> debbugs.gnu.org
Subject: bug#24516: 
Date: Fri, 23 Sep 2016 08:16:52 -0700

On Fri, Sep 23, 2016 at 6:55 AM, Nelson H. F. Beebe <beebe <at> math.utah.edu> wrote:
> Thanks, Jim, for the patch to backref-multibyte-slow; I've applied it
> to a new directory grep-2.25.92-f3e9.p1, and have builds in progress
> now on the Fedora systems.
>
> I think that any kind of wallclock-time-dependent test in a package
> test suite is seriously prone to failure.

Writing portable perf-measuring tests is hard, indeed. I agree they're
prone to failure, *if* we're considering tests with naive absolute
limits. This however was a carefully written test to ensure that the
matcher no longer has O(N^2) behavior, using only relative duration
comparisons. The problem is that I don't want to make the test
duration unnecessarily long. If I didn't mind a longer-duration
initial test (to get a reference time), then there'd be no problem
requiring that the potentially much-longer-in-case-of-regression one
terminates in < 10x that duration.

Anyway, thanks for confirming that this simple fix is probably enough.

> Although some developers
> may have the luxury of a fast personal machine on which nothing else
> is running when a package is built, many of us live in multiuser

These tests are designed not just to work on my systems, but also on
bottom-end molasses-slow m68k simulators.

> environments where the load on the build machines is completely
> unpredictable, and beyond our control.
>
> Also, for someone like me with numerous VMs running on a single
> desktop, parallel builds will certainly drive up the load.  With the
> large number of test systems that I have, there is no reasonable way
> to do the builds sequentially, because such a process could take hours
> to days to complete.

Hah. I would never suggest that you or anyone else run builds/tests
sequentially. I have been militant about making things work in
parallel ever since Roland added job support to GNU make.

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