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Re: [PATCH] Deduce automatically number of cores for -flto option.


On 7/31/19 9:34 AM, Jakub Jelinek wrote:
> On Wed, Jul 31, 2019 at 09:20:40AM +0200, Martin Liška wrote:
>> One possible solution will be to adjust lto.exp:
>>
>> 	  set LTO_OPTIONS [list	\
>> 	      {-O0 -flto -flto-partition=none -fuse-linker-plugin} \
>> 	      {-O2 -flto -flto-partition=none -fuse-linker-plugin -fno-fat-lto-objects } \
>> 	      {-O0 -flto -flto-partition=1to1 -fno-use-linker-plugin } \
>> 	      {-O2 -flto -flto-partition=1to1 -fno-use-linker-plugin } \
>>
>> and replace all -flto with -flto=1. But still, many individual tests set -flto by themselves.
>> Another solution would be to disable the auto-detection with an environment variable:
>>
>> diff --git a/gcc/lto-wrapper.c b/gcc/lto-wrapper.c
>> index 353187c6043..bb6fb2b53ff 100644
>> --- a/gcc/lto-wrapper.c
>> +++ b/gcc/lto-wrapper.c
>> @@ -1423,7 +1423,7 @@ run_gcc (unsigned argc, char *argv[])
>>        auto_parallel = 0;
>>        parallel = 0;
>>      }
>> -  else if (!jobserver && parallel)
>> +  else if (!jobserver && parallel && !getenv ("LTO_NO_AUTO_PARALLEL"))
>>      {
>>        /* If there's no explicit usage of jobserver and
>>  	 parallel is enabled, then automatically detect
>> diff --git a/gcc/testsuite/lib/lto.exp b/gcc/testsuite/lib/lto.exp
>> index 25c934731df..e303894e0b0 100644
>> --- a/gcc/testsuite/lib/lto.exp
>> +++ b/gcc/testsuite/lib/lto.exp
>> @@ -209,6 +209,8 @@ proc lto_init { args } {
>>  	  ]
>>  	}
>>      }
>> +
>> +    setenv LTO_NO_AUTO_PARALLEL 1
>>  }
>>  
>>  #
>>
>> Can you Jakub test the patch or the s/-flto/-flto=1 solutions please?
> 
> Neither will work very well, we have thousands of -flto tests outside of
> lto.exp, e.g. dg-torture.exp (or libgomp and others) cycle through various
> options including -flto etc.
> 
> Some env var would be useful I guess, though shouldn't it have GCC in the
> name?

Works for me.

>  I mean, if we run into these fork-bomb problems in gcc, won't other
> projects run into those as well?

Right now, we build whole openSUSE distribution with -flto=N (N based on # of threads)
and we haven't seen issues related to fork-bomb.

> 
> Why doesn't the jobserver work in the tests?  Is that because of missing +
> somewhere in the Makefiles or is something unsetting MFLAGS or MAKEFLAGS
> env vars?

Is Dejagnu using make internally to invoke individual tests?

> 
> Though, as I said on IRC, I think we might run out of filedescriptors when
> using jobserver too, say if on 64 thread machine one does make -j64 -k check
> and each test simultaneously tries to create 64 partitions, that would be
> 4096 connections to the jobserver, right?
> 
> 	Jakub
> 


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