Sorry, I neglected to include a link to the ticket:
http://dev.clojure.org/jira/browse/CLJ-1296
On Sun, Nov 17, 2013 at 2:11 PM, Andy Fingerhut <[email protected]>wrote:
> 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 <[email protected]>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 <[email protected]
>> > 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 <[email protected]> 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 <[email protected]>
>>> 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 <[email protected]> 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
>>> >>> >
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