Fw: throwing static exceptions sometimes VERY slow!

Thu Mar 2 11:35:20 UTC 2017

Ioi,

Argh, you're right about the formatting.  I'll paste below my last reply to
Jacob.

Instead of overriding fillInStacktrace, which is a synchronized method and
you're sharing those instances between threads, can you construct the
Continue and Break exceptions telling base class that you don't want
writable stacktrace?

The jitter you're seeing could be lock contention due to above, biased lock
revocation, JIT deoptimizations (although in your Test I'm not sure if
it'll deoptimize since the throws are not uncommon).

You can add -XX:+PrintSafepointStatistics
-XX:PrintSafepointStatisticsCount=1 to get reasons for  safepoints printed
to stdout.

As mentioned, run your test with -XX:+PrintCompilation to see if JIT is
doing something.

On Thu, Mar 2, 2017 at 1:12 AM Ioi Lam <ioi.lam at oracle.com> wrote:

> Vitaly,
>
> Thanks for forwarding the email. Unfortunately, the HTML formatting has
> been stripped by the mailing list so it's hard to see who said what :-(
>
> > I made a mockup-test (see attachment) that mimicks kind of what my
> > generated code does and adds measurements before throw and after catch.
> > Mostly, in my experiments with this, the throw takes on average 20 ns,
> > but between a 1 and 3 per million iterations take longer than 1 ms, on
> > average around 7 ms. It can be observed that doing a garbage collection
> in
> > a different java process (namely my eclipse that started the test)
> greatly
> > influences the frequency of the > 1 ms throws, so maybe it is simply a
> load
> > issue. Using multiple threads in parallel also seems to heighten the
>
> Perhaps the slow down is caused by GC?
>
> One simple way to try is to run with different heap sizes, and use
> different type of collectors. If you observe different frequency of the
> outlier cases, then it's probably caused by GC pauses.
>
> Jacob, could you post the mockup test again?
>
> Thanks
> - Ioi
>
> On 3/1/17 4:04 PM, Vitaly Davidovich wrote:
> > +hotspot dev as it got dropped
> >
> > On Wed, Mar 1, 2017 at 7:03 PM Vitaly Davidovich <vitalyd at gmail.com>
> wrote:
> >
> >> Instead of overriding fillInStacktrace, which is a synchronized method
> and
> >> you're sharing those instances between threads, can you construct the
> >> Continue and Break exceptions telling base class that you don't want
> >> writable stacktrace?
> >>
> >> The jitter you're seeing could be lock contention due to above, biased
> >> lock revocation, JIT deoptimizations (although in your Test I'm not
> sure if
> >> it'll deoptimize since the throws are not uncommon).
> >>
> >> You can add -XX:+PrintSafepointStatistics
> >> -XX:PrintSafepointStatisticsCount=1 to get reasons for  safepoints
> printed
> >> to stdout.
> >>
> >> As mentioned, run your test with -XX:+PrintCompilation to see if JIT is
> >> doing something.
> >>
> >> On Wed, Mar 1, 2017 at 7:52 AM Wieland, Jacob <
> Jacob.Wieland at spirent.com>
> >> wrote:
> >>
> >>
> >>
> >>
> >> sorry, forgot the attachment
> >>
> >>
> >> BR
> >>
> >>
> >>
> >> *Dr. Jacob Wieland*
> >>
> >> *Senior Software Engineer*
> >>
> >> main    +49.30.7261919.34
> >>
> >> mobile +49.173.6446443
> >>
> >>
> >> jacob.wieland at spirent.com
> >>
> >>
> >> www.spirent.com
> >>
> >>
> >>
> >>
> >> Follow us on:
> >>
> >>
> >> Spirent Communications
> >>
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> >>
> >> ------------------------------
> >> *From:* Wieland, Jacob
> >> *Sent:* Wednesday, March 1, 2017 1:47:52 PM
> >> *To:* Vitaly Davidovich; David Holmes
> >> *Cc:* hotspot-dev at openjdk.java.net
> >>
> >> *Subject:* Re: throwing static exceptions sometimes VERY slow!
> >>
> >> Hi,
> >>
> >>
> >> here are the general system infos:
> >>
> >>
> >> uname -a:
> >>
> >>
> >> Linux ber-28753 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt20-1+deb8u3
> >> (2016-01-17) x86_64 GNU/Linux
> >>
> >>
> >> lscpu:
> >>
> >>
> >> Architecture:          x86_64
> >> CPU op-mode(s):        32-bit, 64-bit
> >> Byte Order:            Little Endian
> >> CPU(s):                4
> >> On-line CPU(s) list:   0-3
> >> Thread(s) per core:    1
> >> Core(s) per socket:    4
> >> Socket(s):             1
> >> NUMA node(s):          1
> >> Vendor ID:             GenuineIntel
> >> CPU family:            6
> >> Model:                 58
> >> Model name:            Intel(R) Core(TM) i5-3450 CPU @ 3.10GHz
> >> Stepping:              9
> >> CPU MHz:               2094.558
> >> CPU max MHz:           3500.0000
> >> CPU min MHz:           1600.0000
> >> BogoMIPS:              6186.30
> >> Virtualization:        VT-x
> >> L1d cache:             32K
> >> L1i cache:             32K
> >> L2 cache:              256K
> >> L3 cache:              6144K
> >> NUMA node0 CPU(s):     0-3
> >>
> >> java -version:
> >>
> >>
> >> java version "1.8.0_102"
> >> Java(TM) SE Runtime Environment (build 1.8.0_102-b14)
> >> Java HotSpot(TM) 64-Bit Server VM (build 25.102-b14, mixed mode)
> >>
> >> Rest of the answers inline.
> >>
> >> BR
> >>
> >>
> >>
> >> *Dr. Jacob Wieland*
> >>
> >> *Senior Software Engineer*
> >>
> >> main    +49.30.7261919.34
> >>
> >> mobile +49.173.6446443
> >>
> >>
> >> jacob.wieland at spirent.com
> >>
> >>
> >> www.spirent.com
> >>
> >>
> >>
> >>
> >> Follow us on:
> >>
> >>
> >> Spirent Communications
> >>
> >> <https://www.linkedin.com/company/spirent-communications>
> >> <https://www.linkedin.com/company/spirent-communications>|
> >> <https://twitter.com/Spirent> <https://twitter.com/Spirent>|
> >> <https://www.facebook.com/spirent> <https://www.facebook.com/spirent>
> >>
> >>
> >> Michaelkirchstraße 17/18
> >>
> >> 10179 Berlin, Germany
> >>
> >>
> >>
> >> *+++++  N E W S F L A S H  +++++*
> >>
> >>
> >>
> >> Spirent Communications and Testing Technologies join forces to become
> your
> >> test automation power-house. Read more at http://conta.cc/1S62BEY.
> >>
> >> ------------------------------
> >> *From:* Vitaly Davidovich <vitalyd at gmail.com>
> >> *Sent:* Tuesday, February 28, 2017 1:46:09 PM
> >> *To:* David Holmes
> >> *Cc:* Wieland, Jacob; hotspot-dev at openjdk.java.net
> >> *Subject:* Re: throwing static exceptions sometimes VERY slow!
> >>
> >>
> >>
> >> On Tue, Feb 28, 2017 at 7:37 AM, David Holmes <david.holmes at oracle.com>
> >> wrote:
> >>
> >> Hi,
> >>
> >> On 28/02/2017 9:02 PM, Wieland, Jacob wrote:
> >>
> >> Hi,
> >>
> >> I am observing a very strange behavior.
> >>
> >> In our generated code (due to various reasons I won't go into here
> unless
> >> I have to, but trust me, they are legit), we throw static exceptions for
> >> control flow purposes, This seems to work fine and without performance
> loss
> >> most of the time. However, we are observing now that every few seconds,
> a
> >> throw sometimes takes up between 1,5 and 2.5 seconds! (in contrast to
> the
> >> normal almost non-measurable time).
> >>
> >> Update: it seems that the observed behavior was kind of related with
> some
> >> extraneous circumstances (the computer seems to have been more lagged
> than
> >> usual at that point). By now, I can only observe throws that take up to
> 20
> >> milliseconds (which opposed to the normal time still seems slow).
> >>
> >> It does not seem to be GC related, the only idea that I have is the
> jitter.
> >>
> >>
> >> What jitter?
> >>
> >> I'm assuming Jacob is referring to the JIT.  But yes, he needs to
> provide
> >> more information.
> >>
> >> In particular, it would be good to know the following, as David
> mentioned,
> >> (off the top of my head):
> >> 1) JVM cmdline flags
> >>
> >> -Xdebug -Xrunjdwp:transport=dt_socket,address=8001,server=y,suspend=y
> >>
> >> 2) Type of exception thrown (with a stacktrace or not)
> >>
> >> Exception class derived from java.lang.Error that overrides
> >> fillInStackTrace() with 'return this', so stackless. Same instances
> stored
> >> in static final fields are always thrown.
> >>
> >> 3) Is the call stack depth about the same during the slow and fast
> throws?
> >>
> >> It is always exactly the same stack, as it happens in a loop.
> >>
> >> 4) Is the exception thrown frequently or infrequently?
> >>
> >> In the test where this was observed, the exception was thrown every
> 40ms,
> >> so, I guess, frequently.
> >>
> >> 5) Is there -XX:+PrintCompilation output available around the time when
> >> the slowdown is observed
> >>
> >> Unfortunately not, and at the moment, I cannot reproduce the behavior.
> >>
> >> I made a mockup-test (see attachment) that mimicks kind of what my
> >> generated code does and adds measurements before throw and after catch.
> >> Mostly, in my experiments with this, the throw takes on average 20 ns,
> >> but between a 1 and 3 per million iterations take longer than 1 ms, on
> >> average around 7 ms. It can be observed that doing a garbage collection
> in
> >> a different java process (namely my eclipse that started the test)
> greatly
> >> influences the frequency of the > 1 ms throws, so maybe it is simply a
> load
> >> issue. Using multiple threads in parallel also seems to heighten the
> >>
> >> Also, when introducing an additional sleep between iterations (like in
> my
> >> original scenario where I was waiting for a timer to timeout before
> >> executing the construct that used the throw), I cannot reproduce such
> >> outliers at all.
> >>
> >>
> >>
> >> So, my question is. Is this a known (and for some strange reason maybe
> >> even accepted) behavior or is this a bug that I should file with Oracle
> (or
> >> you guys).
> >>
> >>
> >> You really are not giving us anything to go on here. How are you
> observing
> >> this slowness? Exactly how do you throw? What exactly are you measuring?
> >> What's the execution context, the machine, processors etc etc etc.
> >>
> >>
> >> I was observing the slowness in a testcase where I wanted regular
> >> intervals of 40 ms between sending a message via UDP but frequently
> (every
> >> few seconds) got a lag of around 1.5 seconds (and a few days later 0.5
> >> seconds) before the timer which timed out at the correct time was noted.
> >>
> >>
> >> When eliminating one kind of such thrown control exception, the next
> kind
> >> of thrown control exception (from a surrounding construct) was having
> the
> >> same effect which actually led me to the slow-throw-hypothesis.
> Eliminating
> >> all exceptions in the small example confirmed this hypothesis, but going
> >> that route would take a lot of effort for all cases and introduce other
> >> additional imperformances (as I basically have to mock the exception
> >> throwing via cascading return and if-checks on every level) which I
> would
> >> like to avoid.
> >>
> >> Regards,
> >> David
> >>
> >>
> >>
> >>
> >>
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