[x265] Question about CPU addressing (more than 64 logical CPUs)

[Michael Lackner]

Hello again,

My apologies for pushing this (and quoting myself), but it's been a few months, so I
thought I'd try again.

I'm still looking for an answer to the question as to whether x265 can address more than
64 logical processors without NUMA on systems with larger CPU addressing bitvectors, such
as modern FreeBSD UNIX, Windows 10 / Server 2019 and Linux, which have bitvectors 256 bits
wide in their latest versions.

Hardware-wise, an example for such a platform would be a single-socket AMD Threadripper
3990X machine.

Software-wise it'd be interesting for all operating systems without a NUMA API, such as
e.g. FreeBSD UNIX.

Thank you!

On 2020/02/24 10:33, Michael Lackner wrote:
> Hello,
> 
> I've looked through the x265 documentation, and found this for the "-pools" option:
> 
> "In the case that any threadpool has more than 64 threads, the threadpool may be broken
> down into multiple pools of 64 threads each;"
> 
> But that's NUMA-related.
> 
> Now here's the question: How will x265 behave on systems with a flat addressing model (no
> libnuma), but more than 64 logical CPUs? Currently, modern operating system kernels seem
> to have gotten their address bit vectors bumped up from 64 to 256 bits, so users can
> address up to 256 CPUs either without NUMA entirely, or within a single NUMA threadpool.
> 
> Say I have a UNIX machine without NUMA, but with 128 or 256 logical CPUs. How will x265
> behave on such a system? Will it be able to spawn more than 64 threads per process, or not?
> 
> Where I to launch multiple processes of 64 threads each, would the kernel be able to push
> the threads to free CPUs, or does x265 "lock on" to the first 64 forcefully (not sure if
> this is even possible, just asking)?
> 
> Thank you for the clarification!

-- 
Michael Lackner
Lehrstuhl für Informationstechnologie (CiT)
Montanuniversität Leoben
Tel.: +43 3842 402 1505 | Mail: michael.lackner at unileoben.ac.at
Fax.: +43 3842 402 1502 | Web: http://institute.unileoben.ac.at/infotech