Re: [PATCH] pack-bitmap: remove trace2 region from hot path

[Jeff Hostetler <git@jeffhostetler.com>]

On 9/23/22 9:00 AM, Derrick Stolee via GitGitGadget wrote:
> From: Derrick Stolee <derrickstolee@github.com>
> 
> The trace2 region around the call to lazy_bitmap_for_commit() in
> bitmap_for_commit() was added in 28cd730680d (pack-bitmap: prepare to
> read lookup table extension, 2022-08-14). While adding trace2 regions is
> typically helpful for tracking performance, this method is called
> possibly thousands of times as a commit walk explores commit history
> looking for a matching bitmap. When trace2 output is enabled, this
> region is emitted many times and performance is throttled by that
> output.
> 
> For now, remove these regions entirely.
> 
> This is a critical path, and it would be valuable to measure that the
> time spent in bitmap_for_commit() does not increase when using the
> commit lookup table. The best way to do that would be to use a mechanism
> that sums the time spent in a region and reports a single value at the
> end of the process. This technique was introduced but not merged by [1]
> so maybe this example presents some justification to revisit that
> approach.
> 
> [1] https://lore.kernel.org/git/pull.1099.v2.git.1640720202.gitgitgadget@gmail.com/

I'll dust off my "timers and counters" series, address the
various issues that were raised back in December, and resubmit.

Thanks for the reminder.
Jeff