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Summary:
The aim here is to reduce the number of remote memory accesses on
systems with a NUMA memory architecture, typically multi-socket servers.
Linux provides a NUMA API for doing two things:
* Allocating memory local to a particular node
* Binding a thread to a particular node
When given the +RTS --numa flag, the runtime will
* Determine the number of NUMA nodes (N) by querying the OS
* Assign capabilities to nodes, so cap C is on node C%N
* Bind worker threads on a capability to the correct node
* Keep a separate free lists in the block layer for each node
* Allocate the nursery for a capability from node-local memory
* Allocate blocks in the GC from node-local memory
For example, using nofib/parallel/queens on a 24-core 2-socket machine:
```
$ ./Main 15 +RTS -N24 -s -A64m
Total time 173.960s ( 7.467s elapsed)
$ ./Main 15 +RTS -N24 -s -A64m --numa
Total time 150.836s ( 6.423s elapsed)
```
The biggest win here is expected to be allocating from node-local
memory, so that means programs using a large -A value (as here).
According to perf, on this program the number of remote memory accesses
were reduced by more than 50% by using `--numa`.
Test Plan:
* validate
* There's a new flag --debug-numa=<n> that pretends to do NUMA without
actually making the OS calls, which is useful for testing the code
on non-NUMA systems.
* TODO: I need to add some unit tests
Reviewers: erikd, austin, rwbarton, ezyang, bgamari, hvr, niteria
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D2199
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The `nat` type was an alias for `unsigned int` with a comment saying
it was at least 32 bits. We keep the typedef in case client code is
using it but mark it as deprecated.
Test Plan: Validated on Linux, OS X and Windows
Reviewers: simonmar, austin, thomie, hvr, bgamari, hsyl20
Differential Revision: https://phabricator.haskell.org/D2166
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This reverts commit 39b5c1cbd8950755de400933cecca7b8deb4ffcd.
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This will hopefully help ensure some basic consistency in the forward by
overriding buffer variables. In particular, it sets the wrap length, the
offset to 4, and turns off tabs.
Signed-off-by: Austin Seipp <austin@well-typed.com>
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So we can now get these in ThreadScope:
19487000: cap 1: stopping thread 6 (blocked on black hole owned by thread 4)
Note: needs an update to ghc-events. Older ThreadScopes will just
ignore the new information.
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This patch makes two changes to the way stacks are managed:
1. The stack is now stored in a separate object from the TSO.
This means that it is easier to replace the stack object for a thread
when the stack overflows or underflows; we don't have to leave behind
the old TSO as an indirection any more. Consequently, we can remove
ThreadRelocated and deRefTSO(), which were a pain.
This is obviously the right thing, but the last time I tried to do it
it made performance worse. This time I seem to have cracked it.
2. Stacks are now represented as a chain of chunks, rather than
a single monolithic object.
The big advantage here is that individual chunks are marked clean or
dirty according to whether they contain pointers to the young
generation, and the GC can avoid traversing clean stack chunks during
a young-generation collection. This means that programs with deep
stacks will see a big saving in GC overhead when using the default GC
settings.
A secondary advantage is that there is much less copying involved as
the stack grows. Programs that quickly grow a deep stack will see big
improvements.
In some ways the implementation is simpler, as nothing special needs
to be done to reclaim stack as the stack shrinks (the GC just recovers
the dead stack chunks). On the other hand, we have to manage stack
underflow between chunks, so there's a new stack frame
(UNDERFLOW_FRAME), and we now have separate TSO and STACK objects.
The total amount of code is probably about the same as before.
There are new RTS flags:
-ki<size> Sets the initial thread stack size (default 1k) Egs: -ki4k -ki2m
-kc<size> Sets the stack chunk size (default 32k)
-kb<size> Sets the stack chunk buffer size (default 1k)
-ki was previously called just -k, and the old name is still accepted
for backwards compatibility. These new options are documented.
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This replaces the global blackhole_queue with a clever scheme that
enables us to queue up blocked threads on the closure that they are
blocked on, while still avoiding atomic instructions in the common
case.
Advantages:
- gets rid of a locked global data structure and some tricky GC code
(replacing it with some per-thread data structures and different
tricky GC code :)
- wakeups are more prompt: parallel/concurrent performance should
benefit. I haven't seen anything dramatic in the parallel
benchmarks so far, but a couple of threading benchmarks do improve
a bit.
- waking up a thread blocked on a blackhole is now O(1) (e.g. if
it is the target of throwTo).
- less sharing and better separation of Capabilities: communication
is done with messages, the data structures are strictly owned by a
Capability and cannot be modified except by sending messages.
- this change will utlimately enable us to do more intelligent
scheduling when threads block on each other. This is what started
off the whole thing, but it isn't done yet (#3838).
I'll be documenting all this on the wiki in due course.
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