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util: Use steady clock in SeedStrengthen, FindBestImplementation, FlushStateToDisk #27189

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fanquake merged 2 commits into from
Mar 8, 2023
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util: Use steady clock in SeedStrengthen, FindBestImplementation, FlushStateToDisk #27189

fanquake merged 2 commits into from
Mar 8, 2023

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@maflcko maflcko commented Mar 2, 2023 •
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There may be a theoretical deadlock for the duration of the offset when the system clock is adjusted into a past time while executing SeedStrengthen.

Fix this by using steady clock.

Do the same in FindBestImplementation, which shouldn't be affected, because it discards outlier measurements. However, doing the same there for consistency seems fine.

Do the same in FlushStateToDisk, which should make the flushes more steady, if the system clock is adjusted by a large offset.

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DrahtBot commented Mar 2, 2023 •
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ACK john-moffett, willcl-ark
Concept ACK sipa

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@maflcko maflcko changed the title Use steady clock in SeedStrengthen and FindBestImplementation util: Use steady clock in SeedStrengthen and FindBestImplementation Mar 2, 2023
@maflcko maflcko force-pushed the 2303-bench-with-steady-clock- branch from fa29875 to 1111e2f Compare March 2, 2023 13:49
@maflcko maflcko changed the title util: Use steady clock in SeedStrengthen and FindBestImplementation util: Use steady clock in SeedStrengthen, FindBestImplementation, FlushStateToDisk Mar 2, 2023
@DrahtBot DrahtBot mentioned this pull request Mar 2, 2023
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willcl-ark commented Mar 6, 2023

Concept ACK for moving to monotonic clocks.

Am I correct in my understanding that there are no current tests/benchmarks which are calling these while adjusting the system clock, but rather this is additional hardening for a user whose system clock happens to be changed while one of these is executing?

I couldn't easily find any callsites which might be directly affected by this, only indirectly. i.e. The system clock happens to change during a call to GetRandHash() or GetRandBytes() (or similar) resulting in a long or unbounded deadlock whilse the strengthening is taking place.

The only remaining use of GetTimeMicros is now in src/logging.cpp which seems nice.

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maflcko commented Mar 6, 2023

Am I correct in my understanding that there are no current tests/benchmarks which are calling these while adjusting the system clock, but rather this is additional hardening for a user whose system clock happens to be changed while one of these is executing?

yes, I don't think the system clock is ever adjusted in tests. Usually, we'd use NodeClock for a mockable clock. faketime may be a way to mock the system clock in tests, but faketime may not be available on Windows.

About the user-facing changes, this should only be an improvement:

  • RandAddPeriodic is called in the scheduler thread, so it blocking for a long time may also block shutdown, IBD, and other stuff?
  • FindBestImplementation shouldn't have any observable change, as explained in OP
  • FlushStateToDisk should not have any observable change, unless the node crashes, I guess?

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john-moffett approved these changes Mar 6, 2023
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ACK fa1b4e5

Good conceptual change, as there's no reason for (eg) an NTP adjustment to affect these things.

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willcl-ark approved these changes Mar 7, 2023
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ACK fa1b4e5

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sipa commented Mar 7, 2023

Concept ACK

@fanquake fanquake merged commit 2de0559 into bitcoin:master Mar 8, 2023
@maflcko maflcko deleted the 2303-bench-with-steady-clock-🙂 branch March 8, 2023 14:32
sidhujag pushed a commit to syscoin/syscoin that referenced this pull request Mar 8, 2023
@fanquake
Merge bitcoin#27189: util: Use steady clock in SeedStrengthen, FindBe…
24cce59 
…stImplementation, FlushStateToDisk

fa1b4e5 Use steady clock in FlushStateToDisk (MarcoFalke)
1111e2f Use steady clock in SeedStrengthen and FindBestImplementation (MarcoFalke)

Pull request description:

  There may be a theoretical deadlock for the duration of the offset when the system clock is adjusted into a past time while executing `SeedStrengthen`.

  Fix this by using steady clock.

  Do the same in `FindBestImplementation`, which shouldn't be affected, because it discards outlier measurements. However, doing the same there for consistency seems fine.

  Do the same in `FlushStateToDisk`, which should make the flushes more steady, if the system clock is adjusted by a large offset.

ACKs for top commit:
  john-moffett:
    ACK fa1b4e5
  willcl-ark:
    ACK fa1b4e5

Tree-SHA512: cc625e796b186accd53222bd64eb57d0512bc7e588312d254349b542bbc5e5daac348ff2b3b3f7dc5ae0bbbae2ec11fdbf3022cf2164211633765a4b0108e83e
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@stickies-v stickies-v Awaiting requested review from stickies-v

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@willcl-ark willcl-ark willcl-ark approved these changes

@john-moffett john-moffett john-moffett approved these changes

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