That really shouldn't be near system noise for a well constructed
performance test. You might be seeing things like thermal issues, etc
though - good benchmarking is a serious subject.
Also we're not talking wall clock tests, we're talking specific metrics.
The machines do tend to be bare metal, but many of these are entirely CPU
performance independent, memory timing independent, etc. Well not quite but
that's a longer discussion.
The investigation of Haskell code performance is a very good thing to do
BTW, but you'd still want to avoid regressions in the improvements you
made. How well we can do that and the cost of it is the primary issue here.
-davean
On Wed, Mar 17, 2021 at 6:22 PM Karel Gardas
On 3/17/21 4:16 PM, Andreas Klebinger wrote:
Now that isn't really an issue anyway I think. The question is rather is 2% a large enough regression to worry about? 5%? 10%?
5-10% is still around system noise even on lightly loaded workstation. Not sure if CI is not run on some shared cloud resources where it may be even higher.
I've done simple experiment of pining ghc compiling ghc-cabal and I've been able to "speed" it up by 5-10% on W-2265.
Also following this CI/performance regs discussion I'm not entirely sure if this is not just a witch-hunt hurting/beating mostly most active GHC developers. Another idea may be to give up on CI doing perf reg testing at all and invest saved resources into proper investigation of GHC/Haskell programs performance. Not sure, if this would not be more beneficial longer term.
Just one random number thrown to the ring. Linux's perf claims that nearly every second L3 cache access on the example above ends with cache miss. Is it a good number or bad number? See stats below (perf stat -d on ghc with +RTS -T -s -RTS').
Good luck to anybody working on that!
Karel
Linking utils/ghc-cabal/dist/build/tmp/ghc-cabal ... 61,020,836,136 bytes allocated in the heap 5,229,185,608 bytes copied during GC 301,742,768 bytes maximum residency (19 sample(s)) 3,533,000 bytes maximum slop 840 MiB total memory in use (0 MB lost due to fragmentation)
Tot time (elapsed) Avg pause Max pause Gen 0 2012 colls, 0 par 5.725s 5.731s 0.0028s 0.1267s Gen 1 19 colls, 0 par 1.695s 1.696s 0.0893s 0.2636s
TASKS: 4 (1 bound, 3 peak workers (3 total), using -N1)
SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)
INIT time 0.000s ( 0.000s elapsed) MUT time 27.849s ( 32.163s elapsed) GC time 7.419s ( 7.427s elapsed) EXIT time 0.000s ( 0.010s elapsed) Total time 35.269s ( 39.601s elapsed)
Alloc rate 2,191,122,004 bytes per MUT second
Productivity 79.0% of total user, 81.2% of total elapsed
Performance counter stats for '/export/home/karel/sfw/ghc-8.10.3/bin/ghc -H32m -O -Wall -optc-Wall -O0 -hide-all-packages -package ghc-prim -package base -package binary -package array -package transformers -package time -package containers -package bytestring -package deepseq -package process -package pretty -package directory -package filepath -package template-haskell -package unix --make utils/ghc-cabal/Main.hs -o utils/ghc-cabal/dist/build/tmp/ghc-cabal -no-user-package-db -Wall -fno-warn-unused-imports -fno-warn-warnings-deprecations -DCABAL_VERSION=3,4,0,0 -DBOOTSTRAPPING -odir bootstrapping -hidir bootstrapping libraries/Cabal/Cabal/Distribution/Fields/Lexer.hs -ilibraries/Cabal/Cabal -ilibraries/binary/src -ilibraries/filepath -ilibraries/hpc -ilibraries/mtl -ilibraries/text/src libraries/text/cbits/cbits.c -Ilibraries/text/include -ilibraries/parsec/src +RTS -T -s -RTS':
39,632.99 msec task-clock # 0.999 CPUs utilized 17,191 context-switches # 0.434 K/sec
0 cpu-migrations # 0.000 K/sec
899,930 page-faults # 0.023 M/sec
177,636,979,975 cycles # 4.482 GHz (87.54%) 181,945,795,221 instructions # 1.02 insn per cycle (87.59%) 34,033,574,511 branches # 858.718 M/sec (87.42%) 1,664,969,299 branch-misses # 4.89% of all branches (87.48%) 41,522,737,426 L1-dcache-loads # 1047.681 M/sec (87.53%) 2,675,319,939 L1-dcache-load-misses # 6.44% of all L1-dcache hits (87.48%) 372,370,395 LLC-loads # 9.395 M/sec (87.49%) 173,614,140 LLC-load-misses # 46.62% of all LL-cache hits (87.46%)
39.663103602 seconds time elapsed
38.288158000 seconds user 1.358263000 seconds sys _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs