Fwd: [libreoffice-documentation] Multi-threading in Calc

[Drew Jensen]

To follow up on that.

Using LO 6.4 & 7.0 pre-release build on Ubuntu. Recalculating one of the
OpenCL test xls files just now.

Starting up with a command line
MAX_CONCURRENCY=0 ./soffice
Does turn the CPU threading off.

Restarting with a command line
MAX_CONCURRENCY=4 ./soffice
Turns it back on (for my AMD a5800 processor this will give me two threads,
because while the CPU is called a 4 core processor and it does have 4
accumulators it only has 2 floatingpoint cores and this is the limiting
factor it seems) with recalculation time for the workbook is ~2x faster.


On Thu, Apr 23, 2020 at 1:48 PM Drew Jensen <drewjensen.inbox at gmail.com>
wrote:

> BTW I'm copying a paragraph from an email on a different list.
>
> "Also - if you set MAX_CONCURRENCY=16 - or somesuch (ie. twice your
> number of threads) - you may be able to defeat the hyper-threaded
> halving, and see if this workload happens to be one that does better
> with hyper-threading than without."M.M.
>
> It might be worth mentioning the MAX_CURRENCY setting for controlling CPU
> thread usage.
>
> Also, I wonder if the folks answering could answer one other question:
> Does LibreOffice OnLine also use cpu threading in the same way it does
> when run for desktop or headless? It would be with noting in the
> documentation if it does not, IMO.
>
>
>
> On Thu, Apr 23, 2020 at 9:56 AM Stephen Fanning <
> stevemfanning.wh at gmail.com> wrote:
>
>> Mike and  Luboš,
>>
>> Many thanks for your help on this topic.
>>
>> Regards,
>>
>> Steve
>>
>> On Thu, 23 Apr 2020 at 11:16, Mike Kaganski <mikekaganski at hotmail.com>
>> wrote:
>>
>>> On 23.04.2020 13:12, Luboš Luňák wrote:
>>> > On Thursday 23 of April 2020, Stephen Fanning wrote:
>>> >> As for the processing itself, I remain unclear about how Calc
>>> allocates
>>> >> tasks to threads. Can we give the user any general advice on how he
>>> could
>>> >> structure his spreadsheet to gain the maximum performance benefits
>>> from the
>>> >> availability of multiple cores? Or maybe there are ways to organise a
>>> >> spreadsheet that will frustrate Calc's attempts to multi-thread,
>>> which we
>>> >> ought to advise against?
>>> >
>>> >  Technically threads are generally used only for formula groups, which
>>> are a
>>> > sufficient number of adjacent cells in a column that use the same
>>> formula
>>> > (and get different results because of relative cell addressing). In UI
>>> terms,
>>> > write e.g. "=A1*2" to B1, grab the bottom-right corner of the cell and
>>> extend
>>> > down. But it's implementated this way because that's usually how large
>>> > spreadsheets are created. So I think it's a needless complication to
>>> be
>>> > specific about this.
>>> >
>>>
>>> IMO it's still useful to mention that the optimization is column-based.
>>> Because many people don't realize that row-based layout is potentially
>>> less efficient. This would be beneficial to those who don't create
>>> spreadsheets according to how it's "usually" done.
>>>
>>> --
>>> Best regards,
>>> Mike Kaganski
>>>
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>>
>
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