I have just created a ticket linking to this discussion, with a copy of one
of Michal's earlier messages in the thread as a description of what might
be the problem.
I would not say that this is the same as movement on this issue. Movement
in the form that would lead to a change in the Clojure compiler will
require one or more volunteers to carefully diagnose the root cause of the
problem, develop one or more patches, respond to comments from screeners
and/or Rich Hickey, etc. If people want to raise more attention to this
issue, one way to do it is to vote on the ticket in JIRA. If you do not
already have an account, you can create one here:
http://dev.clojure.org/jira/secure/Signup!default.jspa
Andy
On Sun, Nov 17, 2013 at 10:14 AM, Michael Blume <blume.m...@gmail.com>wrote:
> Sorry to be a bother, but any movement on this? This looks like a real
> performance bug and I don't yet have the internals knowledge to chase it
> down myself.
>
>
> On Sun, Nov 3, 2013 at 12:10 PM, Michał Marczyk
> <michal.marc...@gmail.com>wrote:
>
>> Well, that is interesting.
>>
>> The difference between the compiled versions of
>>
>> (defn foo [x]
>> (if (> x 0)
>> (inc x)
>> (locking o
>> (dec x))))
>>
>> and
>>
>> (defn bar [x]
>> (if (> x 0)
>> (inc x)
>> (let [res (locking o
>> (dec x))]
>> res)))
>>
>> is quite significant. foo gets compiled to a single class, with
>> invocations handled by a single invoke method; bar gets compiled to a
>> class for bar + an extra class for an inner function which handles the
>> (locking o (dec x)) part -- probably very similar to the output for
>> the version with the hand-coded locking-part (although I haven't
>> really looked at that yet). The inner function is a closure, so
>> calling it involves an allocation of a closure object; its ctor
>> receives the closed-over locals as arguments and stores them in two
>> fields (lockee and x). Then they get loaded from the fields in the
>> body of the closure's invoke method etc.
>>
>> I guess I'll have to play around with Java equivalents too...
>>
>> Cheers,
>> Michał
>>
>>
>> On 3 November 2013 20:46, Michael Blume <blume.m...@gmail.com> wrote:
>> > I mean, I'm probably being naive, but this suggests that one could write
>> >
>> > (defmacro locking' [& forms]
>> > `(let [res# (locking ~@forms)] res#))
>> >
>> > and use locking' in place of locking for improved performance. Is this
>> > wrong? If it's right, does that suggest the macro in clojure.core
>> should be
>> > changed?
>> >
>> >
>> > On Sun, Nov 3, 2013 at 11:09 AM, Michael Blume <blume.m...@gmail.com>
>> wrote:
>> >>
>> >> Huh, interesting.
>> >>
>> >> I have:
>> >>
>> >> (defn foo' [x]
>> >> (if (> x 0)
>> >> (inc x)
>> >> (let [res (locking o (dec x))] res)))
>> >>
>> >> (defn foo'' [x]
>> >> (if (> x 0)
>> >> (inc x)
>> >> (locking o
>> >> (dec x))))
>> >>
>> >> foo' is fast, but foo'' is slow. So something about wrapping the
>> locking
>> >> clause in a let makes it fast. Still no idea why.
>> >>
>> >> On Sunday, November 3, 2013 9:30:45 AM UTC-8, Michał Marczyk wrote:
>> >>>
>> >>> You have a typo in foo -- monitor-exit's argument is 0 (zero) rather
>> >>> than o (the sentinel object).
>> >>>
>> >>> Besides that, in foo both monitor-enter and monitor-exit get their
>> >>> arguments from a Var. Rewriting to use locking, which first puts the
>> >>> object whose monitor will be used in a local (that is, (let [lockee o]
>> >>> ...), where ... performs the locking using the newly introduced
>> >>> local), gives timings identical to those of bar and baz:
>> >>>
>> >>> (defn foo' [x]
>> >>> (if (> x 0)
>> >>> (inc x)
>> >>> (let [res (locking o (dec x))] res)))
>> >>>
>> >>> So this is one reason not to use monitor-enter and monitor-exit
>> >>> directly. Another reason is that locking guarantees that the monitor
>> >>> will be released (by using try / finally, and of course by preventing
>> >>> situations where the matching monitor-enter & monitor-exit operate on
>> >>> different objects).
>> >>>
>> >>> In fact, both monitor-enter and monitor-exit carry docstrings which
>> >>> explicitly say that they should not be used in user code and point to
>> >>> locking as the user-facing equivalent to Java's synchronized.
>> >>>
>> >>> Cheers,
>> >>> Michał
>> >>>
>> >>>
>> >>> On 1 November 2013 19:34, Michael Blume <blume...@gmail.com> wrote:
>> >>> > https://github.com/MichaelBlume/perf-test
>> >>> >
>> >>> > (ns perf-test
>> >>> > (:use (criterium core))
>> >>> > (:gen-class))
>> >>> >
>> >>> > (def o (Object.))
>> >>> >
>> >>> > (defn foo [x]
>> >>> > (if (> x 0)
>> >>> > (inc x)
>> >>> > (do
>> >>> > (monitor-enter o)
>> >>> > (let [res (dec x)]
>> >>> > (monitor-exit 0)
>> >>> > res))))
>> >>> >
>> >>> > (defn bar [x]
>> >>> > (if (> x 0)
>> >>> > (inc x)
>> >>> > (dec x)))
>> >>> >
>> >>> > (defn locking-part [x l]
>> >>> > (monitor-enter l)
>> >>> > (let [res (dec x)]
>> >>> > (monitor-exit l)
>> >>> > res))
>> >>> >
>> >>> > (defn baz [x]
>> >>> > (if (> x 0)
>> >>> > (inc x)
>> >>> > (locking-part x o)))
>> >>> >
>> >>> > (defn -main []
>> >>> > (println "benching foo")
>> >>> > (bench (foo 5) :verbose)
>> >>> > (println "benching bar")
>> >>> > (bench (bar 5) :verbose)
>> >>> > (println "benching baz")
>> >>> > (bench (baz 5) :verbose)
>> >>> > (println "done benching"))
>> >>> >
>> >>> >
>> >>> >
>> >>> > I'm only ever calling these functions with positive values, so the
>> >>> > monitor-enter branch should never be entered. Nevertheless, the
>> >>> > performance
>> >>> > of foo is much worse than bar or baz.
>> >>> >
>> >>> > The best guess I've got is that the fact that lock-taking is
>> involved
>> >>> > somehow changes how the function is compiled, somehow making the
>> >>> > function
>> >>> > slower. If the practical upshot is that I shouldn't write functions
>> >>> > that
>> >>> > only sometimes lock -- that the locking part of a function should
>> >>> > always be
>> >>> > its own function -- then I can do that, but I'm curious why.
>> >>> >
>> >>> > $ lein uberjar
>> >>> > Compiling perf-test
>> >>> > Created /Users/mike/perf-test/target/perf-test-0.1.0-SNAPSHOT.jar
>> >>> > Created
>> >>> > /Users/mike/perf-test/target/perf-test-0.1.0-SNAPSHOT-standalone.jar
>> >>> > $ java -jar -server target/perf-test-0.1.0-SNAPSHOT-standalone.jar
>> >>> > benching foo
>> >>> > WARNING: Final GC required 1.5974571326266802 % of runtime
>> >>> > x86_64 Mac OS X 10.8.3 4 cpu(s)
>> >>> > Java HotSpot(TM) 64-Bit Server VM 24.0-b28
>> >>> > Runtime arguments:
>> >>> > Evaluation count : 391582560 in 60 samples of 6526376 calls.
>> >>> > Execution time sample mean : 167.426696 ns
>> >>> > Execution time mean : 167.459429 ns
>> >>> > Execution time sample std-deviation : 4.079466 ns
>> >>> > Execution time std-deviation : 4.097819 ns
>> >>> > Execution time lower quantile : 160.742869 ns ( 2.5%)
>> >>> > Execution time upper quantile : 175.453376 ns (97.5%)
>> >>> > Overhead used : 1.634996 ns
>> >>> >
>> >>> > Found 2 outliers in 60 samples (3.3333 %)
>> >>> > low-severe 2 (3.3333 %)
>> >>> > Variance from outliers : 12.5602 % Variance is moderately inflated
>> by
>> >>> > outliers
>> >>> > benching bar
>> >>> > x86_64 Mac OS X 10.8.3 4 cpu(s)
>> >>> > Java HotSpot(TM) 64-Bit Server VM 24.0-b28
>> >>> > Runtime arguments:
>> >>> > Evaluation count : 2174037300 in 60 samples of 36233955 calls.
>> >>> > Execution time sample mean : 26.068923 ns
>> >>> > Execution time mean : 26.066422 ns
>> >>> > Execution time sample std-deviation : 0.887937 ns
>> >>> > Execution time std-deviation : 0.916861 ns
>> >>> > Execution time lower quantile : 23.996763 ns ( 2.5%)
>> >>> > Execution time upper quantile : 27.911936 ns (97.5%)
>> >>> > Overhead used : 1.634996 ns
>> >>> >
>> >>> > Found 3 outliers in 60 samples (5.0000 %)
>> >>> > low-severe 1 (1.6667 %)
>> >>> > low-mild 1 (1.6667 %)
>> >>> > high-mild 1 (1.6667 %)
>> >>> > Variance from outliers : 22.1874 % Variance is moderately inflated
>> by
>> >>> > outliers
>> >>> > benching baz
>> >>> > x86_64 Mac OS X 10.8.3 4 cpu(s)
>> >>> > Java HotSpot(TM) 64-Bit Server VM 24.0-b28
>> >>> > Runtime arguments:
>> >>> > Evaluation count : 2270676660 in 60 samples of 37844611 calls.
>> >>> > Execution time sample mean : 25.834142 ns
>> >>> > Execution time mean : 25.837429 ns
>> >>> > Execution time sample std-deviation : 0.718382 ns
>> >>> > Execution time std-deviation : 0.729431 ns
>> >>> > Execution time lower quantile : 24.837925 ns ( 2.5%)
>> >>> > Execution time upper quantile : 27.595781 ns (97.5%)
>> >>> > Overhead used : 1.634996 ns
>> >>> >
>> >>> > Found 4 outliers in 60 samples (6.6667 %)
>> >>> > low-severe 2 (3.3333 %)
>> >>> > low-mild 2 (3.3333 %)
>> >>> > Variance from outliers : 15.7591 % Variance is moderately inflated
>> by
>> >>> > outliers
>> >>> > done benching
>> >>> >
>> >>> > --
>> >>> > --
>> >>> > You received this message because you are subscribed to the Google
>> >>> > Groups "Clojure" group.
>> >>> > To post to this group, send email to clo...@googlegroups.com
>> >>> > Note that posts from new members are moderated - please be patient
>> with
>> >>> > your
>> >>> > first post.
>> >>> > To unsubscribe from this group, send email to
>> >>> > clojure+u...@googlegroups.com
>> >>> > For more options, visit this group at
>> >>> > http://groups.google.com/group/clojure?hl=en
>> >>> > ---
>> >>> > You received this message because you are subscribed to the Google
>> >>> > Groups
>> >>> > "Clojure" group.
>> >>> > To unsubscribe from this group and stop receiving emails from it,
>> send
>> >>> > an
>> >>> > email to clojure+u...@googlegroups.com.
>> >>> > For more options, visit https://groups.google.com/groups/opt_out.
>> >>
>> >> --
>> >> --
>> >> You received this message because you are subscribed to the Google
>> >> Groups "Clojure" group.
>> >> To post to this group, send email to clojure@googlegroups.com
>> >> Note that posts from new members are moderated - please be patient with
>> >> your first post.
>> >> To unsubscribe from this group, send email to
>> >> clojure+unsubscr...@googlegroups.com
>> >> For more options, visit this group at
>> >> http://groups.google.com/group/clojure?hl=en
>> >> ---
>> >> You received this message because you are subscribed to a topic in the
>> >> Google Groups "Clojure" group.
>> >> To unsubscribe from this topic, visit
>> >> https://groups.google.com/d/topic/clojure/x86VygZYf4Y/unsubscribe.
>> >> To unsubscribe from this group and all its topics, send an email to
>> >> clojure+unsubscr...@googlegroups.com.
>> >>
>> >> For more options, visit https://groups.google.com/groups/opt_out.
>> >
>> >
>> > --
>> > --
>> > You received this message because you are subscribed to the Google
>> > Groups "Clojure" group.
>> > To post to this group, send email to clojure@googlegroups.com
>> > Note that posts from new members are moderated - please be patient with
>> your
>> > first post.
>> > To unsubscribe from this group, send email to
>> > clojure+unsubscr...@googlegroups.com
>> > For more options, visit this group at
>> > http://groups.google.com/group/clojure?hl=en
>> > ---
>> > You received this message because you are subscribed to the Google
>> Groups
>> > "Clojure" group.
>> > To unsubscribe from this group and stop receiving emails from it, send
>> an
>> > email to clojure+unsubscr...@googlegroups.com.
>> > For more options, visit https://groups.google.com/groups/opt_out.
>>
>> --
>> --
>> You received this message because you are subscribed to the Google
>> Groups "Clojure" group.
>> To post to this group, send email to clojure@googlegroups.com
>> Note that posts from new members are moderated - please be patient with
>> your first post.
>> To unsubscribe from this group, send email to
>> clojure+unsubscr...@googlegroups.com
>> For more options, visit this group at
>> http://groups.google.com/group/clojure?hl=en
>> ---
>> You received this message because you are subscribed to a topic in the
>> Google Groups "Clojure" group.
>> To unsubscribe from this topic, visit
>> https://groups.google.com/d/topic/clojure/x86VygZYf4Y/unsubscribe.
>> To unsubscribe from this group and all its topics, send an email to
>> clojure+unsubscr...@googlegroups.com.
>> For more options, visit https://groups.google.com/groups/opt_out.
>>
>
> --
> --
> You received this message because you are subscribed to the Google
> Groups "Clojure" group.
> To post to this group, send email to clojure@googlegroups.com
> Note that posts from new members are moderated - please be patient with
> your first post.
> To unsubscribe from this group, send email to
> clojure+unsubscr...@googlegroups.com
> For more options, visit this group at
> http://groups.google.com/group/clojure?hl=en
> ---
> You received this message because you are subscribed to the Google Groups
> "Clojure" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to clojure+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/groups/opt_out.
>
--
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to clojure+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
