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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
Does turn the CPU threading off.

Restarting with a command line
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 <>

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 <> wrote:

Mike and  Luboš,

Many thanks for your help on this topic.



On Thu, 23 Apr 2020 at 11:16, Mike Kaganski <>

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
tasks to threads. Can we give the user any general advice on how he
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
(and get different results because of relative cell addressing). In UI
write e.g. "=A1*2" to B1, grab the bottom-right corner of the cell and
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
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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