The overhead of measuring SubresourceFiltering performance boils down to the cost of TimeTicks and ThreadTicks Now() method calls, which is significant compared to the cost of subresource load evaluation cost itself.
The idea is to activate performance measurement selectively, according to some policy, e.g., at random for 10% of subresource loads. Ideally the decision to activate should be taken on page-wise basis, i.e. all SubresourceFilter's corresponding to a page should be measuring performance at the same time. This will be especially useful for page-level aggregations to be informative.
Comment 1 by bugdroid1@chromium.org
, Dec 12 2016