GenerateFrame() is scheduled based on vsync CompositorVsyncScheduler. It does not care about Render thread's render frame speed. If a speed of generating frame is faster than a speed of render frame. Render thread could have too many render frame tasks. There is a mechanism of throttling already by DidCompisite. But it seems not work well in some cases.

When soft GL renderer was used, the problem became very serious.

Comment on attachment 8868116 [details] [diff] [review] patch - Throttle GenerateFrame() Review of attachment 8868116 [details] [diff] [review]: ----------------------------------------------------------------- Would like to see this land soon as it fixes a slew of mochitest-media failures. ::: gfx/webrender_bindings/RenderThread.cpp @@ +249,5 @@ > + // Get the old count. > + uint32_t oldCount = 0; > + MOZ_ASSERT(mPendingFrameCounts.Get(AsUint64(aWindowId), &oldCount)); > + if (!mPendingFrameCounts.Get(AsUint64(aWindowId), &oldCount)) { > + return; Might be simpler to move the MOZ_ASSERT to be a "MOZ_ASSERT(false)" inside the if condition. That way you don't do the lookup twice. @@ +263,5 @@ > + // Get the old count. > + uint32_t oldCount = 0; > + MOZ_ASSERT(mPendingFrameCounts.Get(AsUint64(aWindowId), &oldCount)); > + if (!mPendingFrameCounts.Get(AsUint64(aWindowId), &oldCount)) { > + return; Ditto here about the assert

Thanks for the review! I'll update in a next patch.

Pushed by sikeda@mozilla.com: https://hg.mozilla.org/projects/graphics/rev/d1c9dd7d60de Throttle GenerateFrame() r=kats,nical