tags: avoid expensive access to repo.changelog in a loop repo.changelog needs some cache invalidation when run on filtered repository. Accessing it in that loop can be expensive when there is many heads (e.g. mozilla try and it 25 000 heads). Note that the loop itself seems useless, but after this patch it no longer take about ⅛ of the time we spend computing cache for mozilla try. before : ! wall 0.350994 comb 0.350000 user 0.330000 sys 0.020000 (median of 28) after : ! wall 0.319520 comb 0.310000 user 0.290000 sys 0.020000 (median of 30)

blackbox: add a option to duplicate output to stderr too This is useful when debugging some performance operation.

perf: add a --update-last flag to perf::tags See inline documentation for details.

perf: add a `--clear-fnode-cache-rev` argument to perf::tags This will help us test this in situation closer to an update after a commit or a push.