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Wladimir J. van der Laan bc679829e2 Merge #10271 : Use std:🧵:hardware_concurrency, instead of Boost, to determine available cores `937bf4335` Use std:🧵:hardware_concurrency, instead of Boost, to determine available cores (fanquake) Pull request description: Following discussion on IRC about replacing Boost usage for detecting available system cores, I've opened this to collect some benchmarks + further discussion. The current method for detecting available cores was introduced in #6361. Recap of the IRC chat: ``` 21:14:08 fanquake: Since we seem to be giving Boost removal a good shot for 0.15, does anyone have suggestions for replacing GetNumCores? 21:14:26 fanquake: There is std:🧵:hardware_concurrency(), but that seems to count virtual cores, which I don't think we want. 21:14:51 BlueMatt: fanquake: I doubt we'll do boost removal for 0.15 21:14:58 BlueMatt: shit like BOOST_FOREACH, sure 21:15:07 BlueMatt: but all of boost? doubtful, there are still things we need 21:16:36 fanquake: Yea sorry, not the whole lot, but we can remove a decent chunk. Just looking into what else needs to be done to replace some of the less involved Boost usage. 21:16:43 BlueMatt: fair 21:17:14 wumpus: yes, it makes sense to plan ahead a bit, without immediately doing it 21:18:12 wumpus: right, don't count virtual cores, that used to be the case but it makes no sense for our usage 21:19:15 wumpus: it'd create a swarm of threads overwhelming any machine with hyperthreading (+accompanying thread stack overhead), for script validation, and there was no gain at all for that 21:20:03 sipa: BlueMatt: don't worry, there is no hurry 21:59:10 morcos: wumpus: i don't think that is correct 21:59:24 morcos: suppose you have 4 cores (8 virtual cores) 21:59:24 wumpus: fanquake: indeed seems that std has no equivalent to physical_concurrency, on any standard. That's annoying as it is non-trivial to implement 21:59:35 morcos: i think running par=8 (if it let you) would be notably faster 21:59:59 morcos: jeremyrubin and i discussed this at length a while back... i think i commented about it on irc at the time 22:00:21 wumpus: morcos: I think the conclusion at the time was that it made no difference, but sure would make sense to benchmark 22:00:39 morcos: perhaps historical testing on the virtual vs actual cores was polluted by concurrency issues that have now improved 22:00:47 wumpus: I think there are not more ALUs, so there is not really a point in having more threads 22:01:40 wumpus: hyperthreads are basically just a stored register state right? 22:02:23 sipa: wumpus: yes but it helps the scheduler 22:02:27 wumpus: in which case the only speedup using "number of cores" threads would give you is, possibly, excluding other software from running on the cores on the same time 22:02:37 morcos: well this is where i get out of my depth 22:02:50 sipa: if one of the threads is waiting on a read from ram, the other can use the arithmetic unit for example 22:02:54 morcos: wumpus: i'm pretty sure though that the speed up is considerably more than what you might expect from that 22:02:59 wumpus: sipa: ok, I back down, I didn't want to argue this at all 22:03:35 morcos: the reason i haven't tested it myself, is the machine i usually use has 16 cores... so not easy due to remaining concurrency issues to get much more speedup 22:03:36 wumpus: I'm fine with restoring it to number of virtual threads if that's faster 22:03:54 morcos: we should have somene with 4 cores (and actually test it though, i agree 22:03:58 sipa: i would expect (but we should benchmark...) that if 8 scriot validation threads instead of 4 on a quadcore hyperthreading is not faster, it's due to lock contention 22:04:20 morcos: sipa: yeah thats my point, i think lock contention isn't that bad with 8 now 22:04:22 wumpus: on 64-bit systems the additional thread overhead wouldn't be important at least 22:04:23 gmaxwell: I previously benchmarked, a long time ago, it was faster. 22:04:33 gmaxwell: (to use the HT core count) 22:04:44 wumpus: why was this changed at all then? 22:04:47 wumpus: I'm confused 22:05:04 sipa: good question! 22:05:06 gmaxwell: I had no idea we changed it. 22:05:25 wumpus: sigh 22:05:54 gmaxwell: What PR changed it? 22:06:51 gmaxwell: In any case, on 32-bit it's probably a good tradeoff... the extra ram overhead is worth avoiding. 22:07:22 wumpus: https://github.com/bitcoin/bitcoin/pull/6361 22:07:28 gmaxwell: PR 6461 btw. 22:07:37 gmaxwell: er lol at least you got it right. 22:07:45 wumpus: the complaint was that systems became unsuably slow when using that many thread 22:07:51 wumpus: so at least I got one thing right, woohoo 22:07:55 sipa: seems i even acked it! 22:07:57 BlueMatt: wumpus: there are more alus 22:08:38 BlueMatt: but we need to improve lock contention first 22:08:40 morcos: anywya, i think in the past the lock contention made 8 threads regardless of cores a bit dicey.. now that is much better (although more still to be done) 22:09:01 BlueMatt: or we can just merge #10192, thats fee 22:09:04 gribble: https://github.com/bitcoin/bitcoin/issues/10192 \| Cache full script execution results in addition to signatures by TheBlueMatt · Pull Request #10192 · bitcoin/bitcoin · GitHub 22:09:11 BlueMatt: s/fee/free/ 22:09:21 morcos: no, we do not need to improve lock contention first. but we should probably do that before we increase the max beyond 16 22:09:26 BlueMatt: then we can toss concurrency issues out the window and get more speedup anyway 22:09:35 gmaxwell: wumpus: yea, well in QT I thought we also diminished the count by 1 or something? but yes, if the motivation was to reduce how heavily the machine was used, thats fair. 22:09:56 sipa: the benefit of using HT cores is certainly not a factor 2 22:09:58 wumpus: gmaxwell: for the default I think this makes a lot of sense, yes 22:10:10 gmaxwell: morcos: right now on my 24/28 physical core hosts going beyond 16 still reduces performance. 22:10:11 wumpus: gmaxwell: do we also restrict the maximum par using this? that'd make less sense 22:10:51 wumpus: if someone wants to use the virtual cores they should be able to by setting -par= 22:10:51 sipa: flies to US 22:10:52 BlueMatt: sipa: sure, but the shared cache helps us get more out of it than some others, as morcos points out 22:11:30 BlueMatt: (because it means our thread contention issues are less) 22:12:05 morcos: gmaxwell: yeah i've been bogged down in fee estimation as well (and the rest of life) for a while now.. otherwise i would have put more effort into jeremy's checkqueue 22:12:36 BlueMatt: morcos: heh, well now you can do other stuff while the rest of us get bogged down in understanding fee estimation enough to review it 22:12:37 wumpus: [to answer my own question: no, the limit for par is MAX_SCRIPTCHECK_THREADS, or 16] 22:12:54 morcos: but to me optimizing for more than 16 cores is pretty valuable as miners could use beefy machines and be less concerned by block validation time 22:14:38 BlueMatt: morcos: i think you may be surprised by the number of mining pools that are on VPSes that do not have 16 cores 22:15:34 gmaxwell: I assume right now most of the time block validation is bogged in the parts that are not as concurrent. simple because caching makes the concurrent parts so fast. (and soon to hopefully increase with bluematt's patch) 22:17:55 gmaxwell: improving sha2 speed, or transaction malloc overhead are probably bigger wins now for connection at the tip than parallelism beyond 16 (though I'd like that too). 22:18:21 BlueMatt: sha2 speed is big 22:18:27 morcos: yeah lots of things to do actually... 22:18:57 gmaxwell: BlueMatt: might be a tiny bit less big if we didn't hash the block header 8 times for every block. 22:21:27 BlueMatt: ehh, probably, but I'm less rushed there 22:21:43 BlueMatt: my new cache thing is about to add a bunch of hashing 22:21:50 BlueMatt: 1 sha round per tx 22:22:25 BlueMatt: and sigcache is obviously a ton ``` Tree-SHA512: a594430e2a77d8cc741ea8c664a2867b1e1693e5050a4bbc8511e8d66a2bffe241a9965f6dff1e7fbb99f21dd1fdeb95b826365da8bd8f9fab2d0ffd80d5059c		2018-03-06 19:21:34 +01:00
.github	Make default issue text all comments to make issues more readable	2017-11-16 11:50:56 -05:00
.tx	tx: Update transifex slug for 0.16	2018-01-24 16:35:40 +01:00
build-aux/m4	Merge #12294 : [Docs] Create NetBSD build instructions and fix compilation	2018-01-30 09:57:45 +01:00
contrib	Merge #12588 : [Utils] Remove deprecated PyZMQ call from Python ZMQ example	2018-03-06 19:03:13 +01:00
depends	[Depends] Fix Qt build with Xcode 9.2	2018-03-05 13:51:14 -05:00
doc	doc: SIGNER can contains space inside now.	2018-03-06 22:55:16 +08:00
share	Increment MIT Licence copyright header year on files modified in 2017	2018-01-03 02:26:56 +09:00
src	Merge #10271 : Use std:🧵:hardware_concurrency, instead of Boost, to determine available cores	2018-03-06 19:21:34 +01:00
test	Merge #12512 : Don't test against the mempool min fee information in mempool_limit.py	2018-03-05 22:08:19 +01:00
.gitattributes	Separate protocol versioning from clientversion	2014-10-29 00:24:40 -04:00
.gitignore	[build] .gitignore: add QT Creator artifacts	2017-12-22 12:37:00 +01:00
.travis.yml	[tests] Fix names of excluded extended tests for travis	2018-01-29 20:09:15 +10:00
autogen.sh	Add MIT license to autogen.sh and share/genbuild.sh	2016-09-21 23:01:36 +00:00
configure.ac	Merge #12029 : Build: Add a makefile target for Doxygen documentation	2018-02-17 18:49:24 +11:00
CONTRIBUTING.md	[docs] links to code style guides	2017-11-20 13:47:01 +01:00
COPYING	[Trivial] Update license year range to 2018	2018-01-01 04:33:09 +09:00
INSTALL.md	Update INSTALL landing redirection notice for build instructions.	2016-10-06 12:27:23 +13:00
libbitcoinconsensus.pc.in	Unify package name to as few places as possible without major changes	2015-12-14 02:11:10 +00:00
Makefile.am	Build: Add a makefile target for Doxygen documentation	2018-01-25 19:43:19 +01:00
README.md	Rename test/pull-tester/rpc-tests.py to test/functional/test_runner.py	2017-03-20 10:40:31 -04:00

README.md

Bitcoin Core integration/staging tree

https://bitcoincore.org

What is Bitcoin?

Bitcoin is an experimental digital currency that enables instant payments to anyone, anywhere in the world. Bitcoin uses peer-to-peer technology to operate with no central authority: managing transactions and issuing money are carried out collectively by the network. Bitcoin Core is the name of open source software which enables the use of this currency.

For more information, as well as an immediately useable, binary version of the Bitcoin Core software, see https://bitcoin.org/en/download, or read the original whitepaper.

License

Bitcoin Core is released under the terms of the MIT license. See COPYING for more information or see https://opensource.org/licenses/MIT.

Development Process

The master branch is regularly built and tested, but is not guaranteed to be completely stable. Tags are created regularly to indicate new official, stable release versions of Bitcoin Core.

The contribution workflow is described in CONTRIBUTING.md.

The developer mailing list should be used to discuss complicated or controversial changes before working on a patch set.

Developer IRC can be found on Freenode at #bitcoin-core-dev.

Testing

Testing and code review is the bottleneck for development; we get more pull requests than we can review and test on short notice. Please be patient and help out by testing other people's pull requests, and remember this is a security-critical project where any mistake might cost people lots of money.

Automated Testing

Developers are strongly encouraged to write unit tests for new code, and to submit new unit tests for old code. Unit tests can be compiled and run (assuming they weren't disabled in configure) with: make check. Further details on running and extending unit tests can be found in /src/test/README.md.

There are also regression and integration tests, written in Python, that are run automatically on the build server. These tests can be run (if the test dependencies are installed) with: test/functional/test_runner.py

The Travis CI system makes sure that every pull request is built for Windows, Linux, and OS X, and that unit/sanity tests are run automatically.

Manual Quality Assurance (QA) Testing

Changes should be tested by somebody other than the developer who wrote the code. This is especially important for large or high-risk changes. It is useful to add a test plan to the pull request description if testing the changes is not straightforward.

Translations

Changes to translations as well as new translations can be submitted to Bitcoin Core's Transifex page.

Translations are periodically pulled from Transifex and merged into the git repository. See the translation process for details on how this works.

Important: We do not accept translation changes as GitHub pull requests because the next pull from Transifex would automatically overwrite them again.

Translators should also subscribe to the mailing list.