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Update documentation

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Andy Wingo 2024-08-05 15:19:07 +02:00
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11
doc/collector-pcc.md
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@ -24,11 +24,12 @@ entries to the worker's [shared worklist](../src/shared-worklist.h).
When a worker runs out of local work, it will first try to remove work
from its own shared worklist, then will try to steal from other workers.
Because threads compete to evacuate objects, `pcc` uses [atomic
compare-and-swap instead of simple forwarding pointer
updates](./manual.md#forwarding-objects), which imposes around a ~30%
performance penalty. `pcc` generally starts to outperform `scc` when it
can trace with 2 threads, and gets better with each additional thread.
If only one tracing thread is enabled (`parallelism=1`), `pcc` uses
non-atomic forwarding, but if multiple threads compete to evacuate
objects, `pcc` uses [atomic compare-and-swap instead of simple
forwarding pointer updates](./manual.md#forwarding-objects). This
imposes around a ~30% performance penalty but having multiple tracing
threads is generally worth it, unless the object graph is itself serial.
As with `scc`, the memory used for the external worklist is dynamically
allocated from the OS and is not currently counted as contributing to

5
doc/collectors.md
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@ -6,8 +6,7 @@ Whippet has five collectors currently:
- [Serial copying collector (`scc`)](./collector-scc.md): Like `semi`,
but with support for multiple mutator threads.
- [Parallel copying collector (`pcc`)](./collector-pcc.md): Like `scc`,
but with support for multiple tracing threads. Faster than `scc` if
multiple cores are available at collection-time.
but with support for multiple tracing threads.
- [Whippet collector (`whippet`)](./collector-whippet.md):
Immix-inspired collector. Optionally parallel, conservative (stack
and/or heap), and/or generational.
@ -27,6 +26,8 @@ out mutator/embedder bugs. Then if memory is tight, switch to
If you are aiming for maximum simplicity and minimal code size (ten
kilobytes or so), use `semi`.
Only use `scc` if you are investigating GC internals.
If you are writing a new project, you have a choice as to whether to pay
the development cost of precise roots or not. If you choose to not have
precise roots, then go for `stack-conservative-parallel-whippet`