Maciej W. Rozycki wrote:
On Wed, 3 Jan 2024, Hans-Peter Nilsson wrote:
The test execution timeout is different from the tool execution timeout
where it is GCC execution that is being guarded against taking excessive
amount of time on the test host rather than the resulting test case
executable run on the target afterwards, as concerned here. GCC already
has a `dg-timeout-factor' setting for the tool execution timeout, but has
no means to increase the test execution timeout. The GCC side of these
changes adds a corresponding `dg-test-timeout-factor' setting.
Hmm. I think it would be more correct to emphasize that the
existing dg-timeout-factor affects both the tool execution *and*
the test execution, whereas your new dg-test-timeout-factor only
affects the test execution. (And still measured on the host.)
Not really, `dg-timeout-factor' is only applied to tool execution and it
doesn't affect test execution. Timeout value reporting used to be limited
in DejaGNU, but you can enable it easily now by adding the DejaGNU patch
series referred in the cover letter and see that `dg-timeout-factor' is
ignored for test execution.
Then we need a better name for this new feature that more clearly
indicates that it applies to running executables compiled as part of a
test. Also, 'test_timeout' is documented as a knob for site
configuration to twiddle, not for testsuites to adjust. I support
adding scale factors for testsuites to indicate "this test takes longer
than usual" but these will need to be thought through. This quick hack
will cause future maintenance problems.
Usually the compilation time is close to 0, so is this based on
an actual need more than an itchy "wart"?
Or did I miss something?
Compilation is usually quite fast, but this is not always the case. If
you look at the tests that do use `dg-timeout-factor' in GCC, and some
commits that added the setting, then you ought to find actual use cases.
I saw at least one such a test that takes an awful lot of time here on a
reasonably fast host machine and still passes where GCC has been built
with optimisation enabled, but does time out in the compilation phase if
the compiler has been built at -O0 for debugging purposes. I'd have to
chase it though if you couldn't find it as I haven't written the name
down.
So yes, `dg-timeout-factor' does have its use, but it is different from
that of `dg-test-timeout-factor', hence the need for a separate setting.
This name has already caused confusion and the patch has not even been
accepted yet. The feature is desirable but this implementation is not
acceptable.
At the moment, there are two blocking issues with this patch:
1. The global variable name 'test_timeout_factor' is not acceptable
because it has already caused confusion, apparently among GCC developers
who should be familiar with the GCC testsuite. If it already confuses
GCC testsuite domain experts, its meaning is too unclear for general
use. While looking for alternative names, I found the fundamental
problem with this proposed implementation: test phases (such as running
a test program versus running the tool itself) are defined by the
testsuite, not by the framework. DejaGnu therefore cannot explicitly
support this as offered because the proposal violates encapsulation both
ways.
2. New code in DejaGnu using expr(n) is to have the expression braced
as recommended in the expr(n) manpage, unless it actually uses the
semantics provided by unbraced expr expressions, in which case it
*needs* a comment explaining and justifying that.
The second issue is trivially fixable, but the first appears fatal.
There is a new "testcase" mulitplex command in Git master, which will be
included in the next release, that is intended for testsuites to express
dynamic state. The original planned use was to support hierarchical
test groups, for which a "testcase group" command is currently defined.
In the future, dg.exp will be extended to use "testcase group" to
delimit each testcase that it processes, and the framework will itself
explicitly track each test script as a group. (DejaGnu's current
semantics implicitly group tests by test scripts, but only by (*.exp)
scripts.) Could this multiplex be a suitable place to put this API feature?
Using a command also has the advantage that it will cause a hard failure
if the framework does not implement it, unlike a variable that a test
script can set for the framework to silently ignore, leading to
hard-to-reproduce test (timeout) failures if an older framework is used
with a testsuite expecting this feature. The semantics of "testcase
patience" or similar would be defined to extend to the end of the group
(or test script in versions of DejaGnu that do not fully implement
groups) in which it is executed. This limited scope is needed because
allowing timeout scale factors to "bleed over" to the next test script
would play havoc with the planned native parallel testing support, where
the "next" script could have already started in another process.
I suggest a few possible commands off the top of my head:
testcase ask patience WHAT FACTOR
testcase declare patience WHAT FACTOR
testcase patience WHAT FACTOR
The FACTOR is a scale factor, similar to the proposed
'test_timeout_factor' or possibly the keyword "reset" (or special value
0?) to clear a previous factor before leaving a group. Multiple
invocations stack: the effective scale factor is the product of all
applicable scale factors. (This will have straightforward interactions
with groups: leaving a group will restore the scale factor in effect
when the group was entered. The initial scale factor at top-level is 1,
for any WHAT.)
The WHAT is a keyword from a to-be-determined set. There is a
possibility that parts of the framework might eventually respond to
certain WHAT values, but for now, would "dg-run" be suitable to express
a timeout for running a test program and "dg-compile" for the timeout on
running GCC itself? This could lead to reserving dg-* WHAT values for
dg.exp based testsuites to define, with a convention that dg-WHAT scales
the timeout for "dg-do WHAT".
Leaving the definition of WHAT to the testsuite is not an insurmountable
barrier, as providing an inquiry command for the testsuite to use would
not be difficult. This seems to lead towards a "testcase declare
patience WHAT FACTOR" and "testcase inquire patience WHAT" pair. The
former multiplies the current WHAT scale factor by FACTOR, while the
latter returns the appropriate running product.
All this provides a nice way to add upstream support for dg-patience ("{
dg-patience dg-run 3 }" or "{ dg-patience dg-compile 2 }") or a similar
tag to dg.exp, but still leaves the issue of communicating /which/ scale
factor to use to the various command execution procedures. Here we come
back to the same problem, since the current API shape (not changing
anytime soon) does not provide a way to pass a timeout value or scale
factor, other than using a "magic" variable. So we are back to
'timeout_scale_factor', but documented in the procedure documentation
for the remote_* procedures. In this case, the framework could use
uplevel to read the variable as a local variable in the caller's frame,
so the gcc-dg-test procedure would only need to do {set
timeout_scale_factor [testcase inquire patience dg-run]} before using
remote_load to run the test program. (Expect does similar things,
according to its manpage.)
The *_load procedures in the config/*.exp are not documented and
config/README specifically says that they are to be called using the
remote_* procedures. While using a "magic" variable would require some
neat tricks with uplevel/upvar, it should work as long as testsuites use
the documented entrypoints. (The *_load procedures from config/*.exp
are likely to disappear into Tcl namespaces and/or parent interpreters
in the future anyway.)
Comments before I start on an implementation?
-- Jacob
