1496554 - MediaDecoder threads can contend on the allocator lock too much

Status: NEW

(Core :: Audio/Video: Playback, enhancement, P3)

Description

[Randell Jesup [:jesup] (needinfo me)]

See bug 1496096 - decoding many videos at once there causes massive allocator lock contention.  Using the debug patch there in gdb, and breaking 10s apart to monitor the atomics shows a 45% contention rate in the content process.

This means 45% of the time jemalloc tries to lock a mutex, it's owned by someone else and we'll have to wait (spin or otherwise).  Mutex contention at this rate can slow progress to a crawl.  And in other profiles there we see up to 40+ % of the time spent in lll_lock_wait, lll_unlock_wake, pthread_mutex_lock directly, etc.

We should a) try to avoid allocating so much, and b) use per-thread arenas like Stylo does (see https://searchfox.org/mozilla-central/source/layout/style/ServoBindings.cpp#2765)

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

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