N3DS - Performance Issue (maybe related to transparencies)

[MarioKartFan]

On the N3DS, Metal Gear Solid plays at full speed, with virtually no frame drops. Really impressive. There were occasionally some dips in performance (for example, when you enter the Truck next to the Helipad shortly after the start of the game) but after recent commits from @notaz those have been eliminated.

One significant issue that remains, however, is in cutscenes with significant "smoke-like" effects. For example, during the cutscene with Raven, when he fires the cannon and there is a billow of smoke, performance genuinely suffers. Similar impact is felt when the tank treads kick up snow at the start of the cutscene.

I compared the N3DS to my original hardware PSX today, and in that scene alone, the cutscene on the N3DS concludes more than 2 seconds after the cutscene concludes on the original hardware.

Maybe an even better example is after the battle with the tank. When black smoke is billowing out the sides of the tank, Raven's voice stutters repeatedly because the performance is so bad. This continues until the camera cuts away from the smoke.

I do not know if this is the result of some issue specific to the N3DS implementation of Retroarch or if it's an issue with pcsx_rearmed. Last year, Justinweiss speculated that it might be a dynamic recompilation issue. I thought it worth opening an issue here, since recent dynamic recompilation fixes addressed other performance issues on the N3DS. I wonder if this is an issue with pcsx_rearmed that maybe isn't as obvious on higher end devices.

These issues also arise, albeit to a lesser extent, in other games with ice and smoke effects. For example, there are very minor dips in performance of FFIX when certain spell effects appear. Not nearly as severe as the example in Metal Gear Solid though.

Would be incredible if this could get resolved. Happy to paypal someone a coffee (or a month's worth of coffee!) if this one gets resolved.

[notaz]

From your description it sounds GPU related as it happens in scenes with some effects only. So unai plugin would need more optimization, or perhaps trying to use the hardware on 3DS to assist the work (both hard tasks to accomplish).
It's unfortunate they didn't put a Cortex-A series CPU with a NEON unit into N3DS. I wonder how Vita performs there in comparison (which should use the NEON GPU).