[Vm-dev] image format suggestion

tim Rowledge tim at rowledge.org
Sat Sep 14 19:00:13 UTC 2013

On 14-09-2013, at 11:45 AM, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>> Ps also explore the concept of sorting objects based on use profile to cluster usages across pages versus the kind of random layout now. Also could make CPU hw cache logic happier 
> Would this be done off-line as an image-file reoganizer, or on-line by the GC?  If so, got any pointers to issues, approaches, what to optimize etc?  Cheers!

How about using the simulator? Run your application image with a sim jigged to record flags for each long-lived object (I guess you'd actually use them to *discover* the long lived ones…) and then sort by age or hits and see what happens. One probably insane thought (it's early in the morning, give me a break!) but to align objects to make cache lines happy how about a null-object definition? Simply to fill space for alignment, gets skipped and dropped by gc, created at need during compaction? It's a very machine/cpu/os/cache-setup specific issue so it might be hard to even find the best alignments.

tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
"How many Ringworld Engineers does it take to change a lightbulb?" "Thirty. Hey, moving suns around isn't easy..."

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