patch, 2 partsmore t/perf meson/GIT-BUILD-OPTIONS fallout

This series fixes two bugs when trying to use the t/perf/run script to compare two versions of Git.

  [1/2]: t/perf/perf-lib: fix assignment of TEST_OUTPUT_DIRECTORY
  [2/2]: t/perf/run: preserve GIT_PERF_* from environment

 t/perf/perf-lib.sh |  3 ++-
 t/perf/run         | 10 ++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

-Peff

Using the perf suite's "run" helper in a vanilla build fails like this:

  $ make && (cd t/perf && ./run p0000-perf-lib-sanity.sh)
  === Running 1 tests in this tree ===
  perf 1 - test_perf_default_repo works: 1 2 3 ok
  perf 2 - test_checkout_worktree works: 1 2 3 ok
  ok 3 - test_export works
  perf 4 - export a weird var: 1 2 3 ok
  perf 5 - éḿíẗ ńöń-ÁŚĆÍÍ ćḧáŕáćẗéŕś: 1 2 3 ok
  ok 6 - test_export works with weird vars
  perf 7 - important variables available in subshells: 1 2 3 ok
  perf 8 - test-lib-functions correctly loaded in subshells: 1 2 3 ok
  # passed all 8 test(s)
  1..8
  cannot open test-results/p0000-perf-lib-sanity.subtests: No such file or directory at ./aggregate.perl line 159.

It is trying to aggregate results written into t/perf/test-results, but the p0000 script did not write anything there.

The "run" script looks in $TEST_OUTPUT_DIRECTORY/test-results, or if that variable is not set, in test-results in the current working directory (which should be t/perf itself). It pulls the value of $TEST_OUTPUT_DIRECTORY from the GIT-BUILD-OPTIONS file.

But that doesn't quite match the setup in perf-lib.sh (which is what scripts like p0000 use). There we do this at the top of the script:

  TEST_OUTPUT_DIRECTORY=$(pwd)

and then let test-lib.sh append "/test-results" to that. Historically, that made the vanilla case work: we'd always use t/perf/test-results. But when $TEST_OUTPUT_DIRECTORY was set, it would break.

Commit 5756ccd181 (t/perf: fix benchmarks with out-of-tree builds, 2025-04-28) fixed that second case by loading GIT-BUILD-OPTIONS ourselves. But that broke the vanilla case!

Now our setting of $TEST_OUTPUT_DIRECTORY in perf-lib.sh is ignored, because it is overwritten by GIT-BUILD-OPTIONS. And when test-lib.sh sees that the output directory is empty, it defaults to t/test-results, rather than t/perf/test-results.

Nobody seems to have noticed, probably for two reasons:

  1. It only matters if you're trying to aggregate results (like the
     "run" script does). Just running "./p0000-perf-lib-sanity.sh"
     manually still produces useful output; the stored result files are
     just in an unexpected place.

  2. There might be leftover files in t/perf/test-results from previous
     runs (before 5756ccd181). In particular, the ".subtests" files
     don't tend to change, and the lack of that file is what causes it
     to barf completely. So it's possible that the aggregation could
     have been showing stale results that did not match the run that
     just happened.

We can fix it by setting TEST_OUTPUT_DIRECTORY only after we've loaded GIT-BUILD-OPTIONS, so that we override its value and not the other way around. And we'll do so only when the variable is not set, which should retain the fix for that case from 5756ccd181.

Signed-off-by: Jeff King <peff@peff.net>
---
 t/perf/perf-lib.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

If you run:

  GIT_PERF_LARGE_REPO=/some/path ./p1006-cat-file.sh

it will use the repo in /some/path. But if you use the "run" helper script to aggregate and compare results, like this:

  GIT_PERF_LARGE_REPO=/some/path ./run HEAD^ HEAD p1006-cat-file.sh

it will ignore that variable. This is because the presence of the LARGE_REPO variable in GIT-BUILD-OPTIONS overrides what's in the environment. This started with 4638e8806e (Makefile: use common template for GIT-BUILD-OPTIONS, 2024-12-06), which now writes even empty variables (though arguably it was wrong even before with a non-empty value, as we generally prefer the environment to take precedence over on-disk config).

We had the same problem in perf-lib.sh itself, and we hacked around it with 32b74b9809 (perf: do allow `GIT_PERF_*` to be overridden again, 2025-04-04). That's what lets the direct invocation of "./p1006" work above.

And in fact that was sufficient for "./run", too, until it started loading GIT-BUILD-OPTIONS itself in 5756ccd181 (t/perf: fix benchmarks with out-of-tree builds, 2025-04-28). Now it has the same problem: it clobbers any incoming GIT_PERF options from the environment.

We can use the same hack here in the "run" script. It's quite ugly, but it's just short enough that I don't think it's worth trying to factor it out into a common shell library.

In the long run, we might consider teaching GIT-BUILD-OPTIONS to be more gentle in overwriting existing entries. There are probably other GIT_TEST_* variables which would need the same treatment. And if and when we come up with a more complete solution, we can use it in both spots.

Signed-off-by: Jeff King <peff@peff.net>
---
 t/perf/run | 10 ++++++++++
 1 file changed, 10 insertions(+)

Hi Jeff,

On 06/01/2026 10:10 am, Jeff King wrote:

I hesitated to send this email because I have been reduced to simply skimming the git mailing list (very busy with other projects/real life!), and I may have misunderstood what you aim to do here. ;)

In essence, I was triggered by the 'GIT-BUILD-OPTIONS fallout' phrase in the subject line! That reminded me of a problem/patch I was looking at earlier this (wait, last) year. The patch (below) was a complete 'hack' (as you can see) to allow the environment to override the 'GIT-BUILD-OPTIONS' file. This was in an old branch named 'meson-wip' which I have been meaning to look at again to either delete or fix-up.

One of the many reasons (apart from being a disgusting hack) that I didn't progress this patch is because I felt that not all 'options' in that file should be able to be 'overridden'. So, that implies that the file needs to be split into two; one file of options which can be overridden from the environment and one that can't. If so, then someone has to decide which is which.

[I'm sure you could do a much better job than the patch below!]

BTW, I can't remember why I wanted to do this anyway ... :)

Hopefully, this is not a complete waste of the list's time. If so, sorry in advance!

Thanks.

ATB, Ramsay Jones

-------- >8 --------
Date: Tue, 27 May 2025 21:53:49 +0100
Subject: [PATCH] test-lib.sh: allow environment to override GIT-BUILD-OPTIONS

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
---
 t/test-lib.sh | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

On Tue, Jan 06, 2026 at 05:07:11PM +0000, Ramsay Jones wrote:

I think you understood my goal. :) This is more or less what my patch is doing, but just for a select set of options (to un-break t/perf). I think a larger fix may look something like this, but:

  1. I agree with you that we may need to consider which options should
     be able to be overridden and which should not.

  2. This hack has to go everywhere that GIT-BUILD-OPTIONS is read. So
     in test-lib.sh where you have it, but also in perf-lib.sh (matching
     the fix by Dscho earlier) and also in t/perf/run (matching the fix
     here).

It would be nice if we could write GIT-BUILD-OPTIONS in a way that did the right thing. E.g., by writing:

  : ${GIT_FOO:=some-value}

And then the writer (which is the ultimate source of authority for which variables are included) could decide which ones can be overridden.

I _thought_ this wouldn't work because we also source the build options files from the Makefile (and so it has to support both syntaxes). But a quick grep doesn't show us including it. So maybe we used to do so, or maybe I'm mis-remembering (and confusing it with GIT-VERSION-FILE perhaps?).

-Peff