Fix high CPU usage on Linux due to epoll busy-loop#191
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lhoward wants to merge 1 commit intoswhitty:mainfrom
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Fix high CPU usage on Linux due to epoll busy-loop#191lhoward wants to merge 1 commit intoswhitty:mainfrom
lhoward wants to merge 1 commit intoswhitty:mainfrom
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Three fixes for 100% CPU spinning when HTTPServer is idle on Linux: 1. Use edge-triggered (EPOLLET) mode for all sockets, not just the canary eventfd. Level-triggered epoll causes epoll_wait() to return immediately when the listening socket is readable, creating a busy loop. 2. Change accept() to wait on .read events only instead of .connection ([.read, .write]). A listening socket is always writable (EPOLLOUT), so registering for write events causes immediate spurious wakeups. accept() only needs readability (a pending connection). 3. Skip redundant epoll_ctl(EPOLL_CTL_MOD) calls when the event mask hasn't changed. EPOLL_CTL_MOD re-arms edge-triggered events and can cause spurious wakeups when the condition is already met. Fixes: swhitty#186
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #191 +/- ##
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Coverage 92.80% 92.80%
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Files 68 68
Lines 3448 3448
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Hits 3200 3200
Misses 248 248 ☔ View full report in Codecov by Sentry. |
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NB: these fixes were generated by AmpCode. They appear to fix the issue and also do not break tests.
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Three fixes for 100% CPU spinning when HTTPServer is idle on Linux:
Use edge-triggered (EPOLLET) mode for all sockets, not just the canary eventfd. Level-triggered epoll causes epoll_wait() to return immediately when the listening socket is readable, creating a busy loop.
Change accept() to wait on .read events only instead of .connection ([.read, .write]). A listening socket is always writable (EPOLLOUT), so registering for write events causes immediate spurious wakeups. accept() only needs readability (a pending connection).
Skip redundant epoll_ctl(EPOLL_CTL_MOD) calls when the event mask hasn't changed. EPOLL_CTL_MOD re-arms edge-triggered events and can cause spurious wakeups when the condition is already met.
Fixes: #186