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Re: [PATCH 4/2] grep: turn off threading for non-worktree

From
René Scharfe <rene.scharfe@lsrfire.ath.cx>
Date
Dec 7, 2011, 17:00 UTC
Message-ID
<4EDF9BA0.2080204@lsrfire.ath.cx>
In-Reply-To
<201112070912.54766.trast@student.ethz.ch>
Am 07.12.2011 09:12, schrieb Thomas Rast:
Show 20 quoted lines
> René Scharfe wrote:
>> diff --git a/Documentation/git-grep.txt b/Documentation/git-grep.txt
>> index 47ac188..e981a9b 100644
>> --- a/Documentation/git-grep.txt
>> +++ b/Documentation/git-grep.txt
>> @@ -228,8 +228,9 @@ OPTIONS
>>  	there is a match and with non-zero status when there isn't.
>>  
>>  --threads <n>::
>> +	Run <n> search threads in parallel.  Default is 8 when searching
>> +	the worktree and 0 otherwise.  This option is ignored if git was
>> +	built without support for POSIX threads.
> [...]
>> -		nr_threads = (online_cpus() > 1) ? THREADS : 0;
>> +		nr_threads = (online_cpus() > 1 && !list.nr) ? THREADS : 0;
> 
> It would be more consistent to stick to the pack.threads convention
> where 0 means "all of my cores", so to disable threading the user
> would set the number of threads to 1.  Or were you trying to measure
> the contention between the worker thread and the add_work() thread?

Yes, indeed, the cost for the threading overhead does interest me. The documentation should perhaps mention --no-threads explicitly to avoid confusion.

Currently there is no way to specify "as many threads as there are cores" here. Previous measurements indicated that it wasn't too useful, however, because I/O parallelism was beneficial even for machines with less than eight cores and more threads didn't pay off.

René
Previous: Thomas RastNext: Pete Wyckoff
Message 15 of 35 in “grep multithreading and scaling”
  1. 0/3 grep multithreading and scalingThomas Rast, Dec 2, 2011
  2. 1/3 grep: load funcname patterns for -WThomas Rast, Dec 2, 2011
  3. 2/3 grep: enable threading with -p and -W using lazy attribute lookupThomas Rast, Dec 2, 2011
  4. 3/3 grep: disable threading in all but worktree caseThomas Rast, Dec 2, 2011
  5. René ScharfeDec 2, 2011
  6. Thomas RastDec 5, 2011
  7. René ScharfeDec 6, 2011
  8. 4/2 grep: turn off threading for non-worktreeRené Scharfe, Dec 6, 2011
  9. Jeff KingDec 7, 2011
  10. René ScharfeDec 7, 2011
  11. Jeff KingDec 7, 2011
  12. J. Bruce FieldsDec 7, 2011
  13. Jeff KingDec 7, 2011
  14. Thomas RastDec 7, 2011
  15. René ScharfeDec 7, 2011
  16. Pete WyckoffDec 10, 2011
  17. René ScharfeDec 12, 2011
  18. Jeff KingDec 7, 2011
  19. René ScharfeDec 7, 2011
  20. Jeff KingDec 7, 2011
  21. Thomas RastDec 7, 2011
  22. René ScharfeDec 7, 2011
  23. Ævar Arnfjörð BjarmasonDec 23, 2011
  24. Thomas RastDec 23, 2011
  25. Ævar Arnfjörð BjarmasonDec 24, 2011
  26. Jeff KingDec 24, 2011
  27. Nguyen Thai Ngoc DuyDec 24, 2011
  28. Nguyen Thai Ngoc DuyDec 24, 2011
  29. Jeff KingDec 24, 2011
  30. Nguyen Thai Ngoc DuyDec 25, 2011
  31. Jeff KingDec 2, 2011
  32. Thomas RastDec 5, 2011
  33. Thomas RastDec 5, 2011
  34. Jeff KingDec 6, 2011
  35. Eric HermanDec 2, 2011

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