On Thursday, August 26, 2010 21:40:13 Steve Longerbeam wrote: > On 08/26/2010 06:07 PM, Mike Frysinger wrote: > > have you done performance measurements to see the overhead with the MPU > > turned on in your scheme compared to off ? doing something like a > > ffmpeg decode to another file. if the performance trade offs of your > > current scheme (per- mapping) is significant compared to the classic > > per-page, then it is worth while to extend the MPU Kconfig option so > > people can select per-page or per- mapping schema. > > yes, if performance degrades a lot for per-page compared to my current > scheme, that would be worthwhile to offer both options. OTOH, other > people may have different requirements (better protection being more > important than memory footprint or performance, or vice-versa). So it > might make sense to offer both options anyway.
iirc, in the tests we did, doing a cpu intensive task didnt suffer all that much. but doing a memory intensive task (like ffmpeg decoding), we saw a ~10x slowdown :(. so we default it to off but keep it around for debugging since the performance is certainly good enough for that. however, we also didnt profile the whole stack, so there might be some places we can squeeze a bit more performance out. -mike
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