turbo-tasks: add info_span for blocking waits during task restore#92878
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Merging this PR will improve performance by 3.34%
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lukesandberg
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Apr 16, 2026
This was referenced Apr 23, 2026
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What?
Adds a
tracing::info_span!("blocking")aroundlistener.wait()calls inExecuteContextImpl::task()when a task is still being restored from backing storage.Why?
When a task is locked for restoration by another thread, the current thread spins in a loop and calls
listener.wait()until notified. CPU time accounting treats this waiting time as active CPU usage, which skews profiling results.By wrapping the wait in a
"blocking"span, the tracing infrastructure can correctly exclude this idle blocking time from CPU time — ensuring CPU metrics reflect actual computation rather than time spent waiting for another thread to finish restoring a task.How?
Import
tracing::info_spanand enter a"blocking"span immediately beforelistener.wait()in the restore-wait loop inturbopack/crates/turbo-tasks-backend/src/backend/operation/mod.rs. The span is dropped when the wait returns (or when the loop continues to re-check the condition).