[x265] Question about NUMA and core/thread use

[Pradeep Ramachandran]

Michael,
Adding --lookahead-threads 2 statically allocated two threads for
lookahead. Therefore, the worker threads launched to work on WPP will 32-2
= 30 in count. We've found some situations in which statically allocating
threads for lookahead was useful and therefore decided to expose it to the
user. Please see if this helps your use-case and enable appropriately.

Now as far as scaling up for 8K goes, a single instance of x265 scales up
well to 25-30 threads depending on the preset you're running in. We've
found pmode and pme help performance considerably on some Broadwell server
systems but again, that is also dependent on content. I would encourage you
play with those settings and see if they help your use case. Beyond these
thread counts, one instance of x265 may not be beneficial for you.

Pradeep.

On Fri, May 5, 2017 at 3:26 PM, Michael Lackner <
michael.lackner at unileoben.ac.at> wrote:

> I found the reason for "why did x265 use 30 threads and not 32, when I
> have 32 CPUs".
>
> Actually, it was (once again) my own fault. Thinking I know better than
> x265, I spawned
> two lookahead threads starting with 32 logical CPUs ('--lookahead-threads
> 2').
>
> It seems what x265 does is to reserve two dedicated CPUs for this, but
> then it couldn't
> permanently saturate them.
>
> I still don't know when I should be starting with that stuff for 8K
> content. 64 CPUs? 256
> CPUs? Or should I leave everything to x265? My goal was to be able to
> fully load as many
> CPUs as possible in the future.
>
> In any case, the culprit was myself.
>
> On 05/04/2017 11:18 AM, Mario *LigH* Rohkrämer wrote:
> > Am 04.05.2017, 10:58 Uhr, schrieb Michael Lackner <
> michael.lackner at unileoben.ac.at>:
> >
> >> Still wondering why not 32, but ok.
> >
> > x265 will calculate how many threads it will really need to utilize the
> WPP and other
> > parallelizable steps, in relation to the frame dimensions and the
> complexity. It may not
> > *need* more than 30 threads, would not have any task to give to two
> more. Possibly.
> > Developers know better...
>
> --
> Michael Lackner
> Lehrstuhl für Informationstechnologie (CiT)
> Montanuniversität Leoben
> Tel.: +43 (0)3842/402-1505 | Mail: michael.lackner at unileoben.ac.at
> Fax.: +43 (0)3842/402-1502 | Web: http://institute.unileoben.ac.
> at/infotech
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