On Wed, Aug 17, 2016 at 1:31 PM, Páll Haraldsson <pall.haralds...@gmail.com>
wrote:
> On Tuesday, August 16, 2016 at 1:41:54 PM UTC, Erik Schnetter wrote:
>>
>> ```Julia
>> Pkg.add("Hwloc")
>> using Hwloc
>> topo = load_topology()
>> print(topo)
>> ```
>>
>> I just see that Hwloc has problems with Julia 0.5; I'll tag a new release.
>>
>
> Great to know about the hwloc package and its wrapper (I was going to post
> some links on dynamically finding out.. or statically for Linux) .
>
> I did notice however:
>
> "Remove non-functional Windows support
> <https://github.com/JuliaParallel/Hwloc.jl/commit/5cc4f3c3bd20237f82a6ad300b5df94c8d2798b5>"
> (just in the wrapper, the base library supports Windows, so you could add
> suport.. and that commit helps knowing how).
>
> [I didn't check FreeBSD (or OS X) support, is it compatible with Linux?]
>
Yes, it works on all Unix systems I tried. The code to determine the L1
cache size is the same on Windows as on Unix. The problem is just that I
don't know how to build the hwloc library on Windows, or how to install a
pre-built one. This is not a difficult problem, I just didn't have a need
for this.
I was looking into this myself a while back (and getting cache-line size).
> I guess a default fallback of at least 4 KB, possibly 32 KB, might be ok
> (and 16-byte cache lines, probably save and lowest/most common size) on
> case your library finds nothing, e.g. on Windows. [BLAS is compiled, I
> think with cache knowledge, maybe there's a way of knowing dynamically with
> what options? I guess not good to rely on, think it's stipped out in
> Julia-lite branch.]
>
Current (and many former) Intel CPUs use an L1 data cache size with 32
kByte, with cache lines of 64 Bytes.
Depending on your application, it is safer to over-estimate the cache line
size, for example if you need to prevent accessing the same cache line from
multiple threads.
-erik
[I was also thinking ahead to AOT compiled Julia.. be aware of that also..
> when cross-compiling Julia and C++ would seem to have to be conservative,
> one reason Julia seems better than C++ (even without AOT).]
>
>
> See here for save lowest-L1 size you want to support (I've never heard of
> lower than 4 KB data, all shared code+data gone and also where 4 KB):
>
> https://en.wikipedia.org/wiki/List_of_ARM_microarchitectures
>
>
> >is there a (cross-platform) way to get the CPU L1 cache size
>
> You assume you have a [L1] cache..? :) My/the first ARM had none.. than
> came 4 KB (shared, later split and more than L1). Yes, all computers in
> decades have a cache, except for newest fastest TOP500 supercomputer
> (scratchpad, Adapteva's CPU similar) and Tera had just many threads..
>
> --
> Palli.
>
>
>
>>
>> -erik
>>
>>
>> On Tue, Aug 16, 2016 at 5:12 AM, Oliver Schulz <oliver...@tu-dortmund.de>
>> wrote:
>>
>>> Hi,
>>>
>>> is there a (cross-platform) way to get the CPU L1 cache size from Julia?
>>> I'd like to determine the optimal block size(s) for an array algorithm.
>>>
>>>
>>> Cheers,
>>>
>>> Oliver
>>>
>>>
>>
>>
>> --
>> Erik Schnetter <schn...@gmail.com> http://www.perimeterinstitute.
>> ca/personal/eschnetter/
>>
>
--
Erik Schnetter <schnet...@gmail.com>
http://www.perimeterinstitute.ca/personal/eschnetter/
