On 2024-02-26 Sebastian Andrzej Siewior wrote:
> Print the warning about reduced threads only if number is selected
> - automatically and asked to be verbose (-v)
> - explicit by the user
Thanks for the patch! We discussed a bit on IRC and everyone thinks
it's on the right track but we are pondering the implementation details
still.
The thread count messages are shown in situations which don't affect
the compressed output, and thus the importance of these messages isn't
so high. Originally they were there to reduce the chance of people
asking why xz isn't using as many threads as requested.
We are considering to simply change those two message() calls to always
use V_VERBOSE or V_DEBUG instead of the current V_WARNING. So automatic
vs. manual number of threads wouldn't affect it like it does in your
patch. Comparing your apporach and this simpler one:
+ There are scripts that take a user-specified number for
parallelization and that number is passed to multiple tools, not
just xz. Keeping xz -T16 silent about thread count reduction can
make sense in this case.
- The silencing could be done with -q as well though.
There are pros and cons between V_VERBOSE and V_DEBUG.
For (de)compression, a single -v sets V_VERBOSE and actives the
progress indicator. If the thread count messages are shown at -v, on
some systems progress indicator usage would get the message about
reduced thread count as well.
+ It works as a hint that increasing the memory usage limits manually
might allow more threads to be used.
- If one uses progress indicator frequently, the thread count
reduction message might become slightly annoying as the information
is already known by the user.
- Progress indicator can be used in non-interactive cases (when
stderr isn't a terminal). Then xz only prints a final summary per
file. This likely is not a common use case but the thread count
messages would be here as well.
V_DEBUG is set when -v is used twice (-vv).
+ Regular progress indicator uses wouldn't get extra messages.
- A larger number of users might not become aware that they aren't
getting as many threads as they could because the automatic memory
usage limit is too low to allow more threads.
There are also messages that are shown when memory limit does affect
compressed output (switching to single-threaded mode and LZMA2
dictionary size adjustment). The verbosity requirement of these messages
isn't being changed now.
--
Lasse Collin
