Skip sending ETW trace event for nested lock which is always granted automatically #1301
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…automatically. Asking nested lock was not considered to be costly, but sending extra ETW event makes them to pop in performance traces. Since they don't provide much value to understand those traces, we should suppress them. (Note: we don't send ETW when lock is released, so there is no work there.)
AArnott
approved these changes
Apr 18, 2024
This was referenced Aug 7, 2025
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Asking nested lock was not considered to be costly, but sending extra ETW event makes them to pop in performance traces. Since they don't provide much value to understand those traces, we should suppress them.
(Note: we don't send ETW when lock is released, so there is no work there.)
The reason behind this change is that this specific ETW event sometime is the primary delay of certain code path, and sometime could cause incorrect interpreting the trace.
During around 7s solution loading trace, the total thread delay from ETW events is about 1.8s, and this event contributed 0.8s, 2x more than any other events. Because capturing stack of ordinal nested lock does not provide lots of value, i think we should suppress it. It would still send event for all top level locks and when an upgradable lock becomes a write lock.
Note: the real CPU usage in VS is much lower, the overhead is mostly when the system collects stacks during capturing the event. It adds extra time to the code path, instead of direct CPU usage.