Tracy profiler showing the duration distribution of dropping shm pools. ~1 ms is taken by munmap() and the remaining ~6 ms is taken by close() of the file descriptor.

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   Ivan Molodetskikh (yalter@mastodon.online)'s status on Wednesday, 01-Nov-2023 08:46:58 JST Ivan Molodetskikh

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   Today in Wayland compositor profiling! Turns out closing a shm pool file descriptor can result in a fat stall of up to like 6 ms with the kernel waiting on some spinlocks. Which is extra fun when you realize it covers the entire frame budget of your 165 Hz screen, and some clients are sometimes doing it every frame!

   I'm trying a "dropping thread" workaround where the fd closing happens on a separate thread. Appears to work at the first glance.