calicoding
Ok I wasn’t sure at first, but it seems like the performance issue I’m facing is partially due to ref counting. It’s not free!
I’m working in a system I didn’t design, that relies heavily on reference types and inheritance. Given the chance, I probably would have designed it differently, leaning more on value types.
Helge Heß
@joe @mattiem @calicoding Even if there is some atomic instruction doing the thing, the cores would still have to synchronize ie flush their pipelines, no? I don’t know much about such low levels and some info why it isn’t expensive would be welcome 🙃
Or how expensive compared to a simple rc++ increment.
My assumption is that RC is massively more expensive, is that wrong?
Joe Groff
@helge @mattiem @calicoding the particular instructions used for refcounting get speculatively executed as if they were nonatomic, so in the case where there's no contention, there's very little overhead (because the atomic codegen still needs more instructions than a nonatomic update, etc.) if it turns out later the memory location was contended then you throw all that work away and do it properly
Helge Heß
@mattiem @calicoding Ref counting actually is expensive because it is thread safe, it’s the global interpreter lock of Swift.
(and it doesn’t just affect user types, all the cow types use it)
Joe Groff
@helge @mattiem @calicoding on Apple Silicon™️, the expensiveness is at least only if you have actual contention accessing the refcount
Matt Massicotte
@calicoding I saw your first post and was like “hmmmmm”, but this makes more sense
calicoding
LOL so yes ref counting was a bottle neck, but only because I’m an idiot and accidentally called my heavy quadratic calculation hundreds of times more than I needed to 🤦♂️
I wish this was easier to see in the profiler. But also: check your assumptions!
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.