927ab67f27
Since a GC with accounting doesn't run in parallel, it discards owner-thread information (ironically) that is used for parallel collection. Losing ownership information could reduce parallelism in later collections --- but only if they run without accounting. This commit does not turn on ownership tracking, however, because experiments suggest that it isn't worthwhile for Racket: * Preserving ownership information slows down a major collection in accounting mode by 5-10%. * Racket uses accounting mode only for full collections, and the loss of ownership information would mostly affect only later full collections. Since accounting momde tends to stick around, very little parallelism is actually lost. * Without further work, accounting mode cannot benefit from parallelization, because it works by stepping sequentially through accounting domains, and that aligns with thread ownership. A possible improvement is to look ahead in the accounting-domain object sequence to find one that starts in another ownership domain, and then constrain concurrent tracing from that object to keep the count private and not leave the ownership domain until the accounting sequence has caught up. Besides making it easier to turn on "parallel" collection for accounting mode, the small refactorings here make it easier to bring more things, like guardian and weak-pair handling, into the parallel part of a collection. So, the changes are probably worth keeping for that purpose. |
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| README.md | ||
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