2011/4/29 Alexandre Bergel <[email protected]>: >> One silly idea while reading this thread (not the paper): >> For single core, the idea makes sense. >> It may even extend easily to multicore VM (just forget about Smalltalk >> for a while) by counting message sent per core and taking the max. > > But you are here assuming that all the CPU have the same speed > (#messages/sec) right? > > Alexandre >
Sure, an obvious limitation... >> >> Nicolas >> >> 2011/4/29 Alexandre Bergel <[email protected]>: >>> +1 >>> >>> Alexandre >>> >>> >>> On 28 Apr 2011, at 17:35, Michael Haupt wrote: >>> >>>> Hi Alex, >>>> >>>> On 29 April 2011 00:08, Alexandre Bergel <[email protected]> wrote: >>>>>> I think you're being a bit harsh on stack sampling there. It is exact >>>>>> enough to drive optimisation in some really high-performance VMs. It >>>>>> is also deterministic enough to yield data leading to very good >>>>>> performance results in those VMs. Whether focusing on counting >>>>>> messages instead of taking samples is more beneficial would have to be >>>>>> determined by experiment ... >>>>> >>>>> Yes, 25 pages of experiment :-) >>>> >>>> oh, I was not referring to your paper. I was referring to the general >>>> applicability of message counting as opposed to sampling. The latter >>>> is true-and-tried in many high performance VMs. For the former, an >>>> experiment has yielded good results (from what I take from this thread >>>> - I still haven't read your paper, sorry, it's on top of the pile) in >>>> a constrained setting. All I was saying is that it is not possible to >>>> conclude anything for the broader area from the experiments you >>>> conducted. But we're probably of the same opinion here. >>>> >>>>>> What you mean with "non-portable" I do not understand. >>>>> >>>>> The information about the execution time contained in your profile cannot >>>>> be compared with a new profile realized on a different machine, with a >>>>> different CPU. >>>> >>>> That is correct, but the approach itself is portable - may I quote >>>> you: "Most profilers, including MessageTally, count stack frames at a >>>> regular interval. This is doomed to be inexact, non-deterministic and >>>> non-portable". You weren't talking about the results. Those are >>>> obviously specific to the platform, clock frequency, L1/L2/L3 cache >>>> and memory sizes, application input (!) and other factors. >>>> >>>> Best, >>>> >>>> Michael >>>> >>> >>> -- >>> _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: >>> Alexandre Bergel http://www.bergel.eu >>> ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;. >>> >>> >>> >>> >>> >>> >>> >> > > -- > _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: > Alexandre Bergel http://www.bergel.eu > ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;. > > > > > > >
