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Re: bugs to fix before 4.4.0 release

From: Carlo De Falco
Subject: Re: bugs to fix before 4.4.0 release
Date: Thu, 4 Jan 2018 15:25:28 +0000

> On 4 Jan 2018, at 16:07, John W. Eaton <address@hidden> wrote:
> On 01/03/2018 07:09 PM, Michael D Godfrey wrote:
>> Just for information, I get a very similar ratio for dev/4.2.1. This
>> is a bigger jump than in the past. My system is an Intel NUC7i5BNH,
>> i.e. I7 CPU.
>> I tried a few modifications, but the ratio stayed about the same.
>> Also, CPU usage (on 1 processor) was at just about 100% for the whole time 
>> in all
>> cases.
>> Is it not possible to get a trace on just  the a = a + b + 123.0 sequence?
> I haven't done any real profiling, but from my tests it looks like the 
> evaluation of the expression is the real problem.  Comparing
>  t0=tic; for i=1:1000; for j=1:1000; end; end; t1=toc(t0); t1
> in 4.2.1 and the current dev version I see nearly identical results. Both 
> were built with GCC 7.2.0 on a Debian system.
> jwe

indeed the nested loop seems not to be related with the slowdown, 
the following test with a single loop shows the same problem.

 a = b = 1; ii = 1; tic; while (ii++ < 1e6), a = a + b + 123; end; toc

here are results on macos high sierra for octave self compiled with clang++ 
(Apple LLVM version 9.0.0 (clang-900.0.38))

  Elapsed time is 2.59538 seconds.

  Elapsed time is 7.86283 seconds.

a 3x slowdown ...

using "+=" results in a small but consistently reproducible improvement in both 
but the ratio between the two is even increased.

  Elapsed time is 1.86918 seconds.

  Elapsed time is 6.45173 seconds.


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