GCC Multi-Threading Ideas

Nicholas Krause xerofoify@gmail.com
Fri Jan 24 18:51:00 GMT 2020

On 1/24/20 3:18 AM, Allan Sandfeld Jensen wrote:
> On Freitag, 24. Januar 2020 04:38:48 CET Nicholas Krause wrote:
>> On 1/23/20 12:19 PM, Nicholas Krause wrote:
>>> On 1/23/20 3:39 AM, Allan Sandfeld Jensen wrote:
>>>> On Montag, 20. Januar 2020 20:26:46 CET Nicholas Krause wrote:
>>>>> Greetings All,
>>>>> Unfortunately due to me being rather busy with school and other
>>>>> things I
>>>>> will not be able to post my article to the wiki for awhile. However
>>>>> there is a  rough draft here:
>>>>> https://docs.google.com/document/d/1po_RRgSCtRyYgMHjV0itW8iOzJXpTdHYIpC9
>>>>> gUMj
>>>>> Oxk/edit that may change a little for people to read in the meantime.
>>>> This comment might not be suited for your project, but now that I
>>>> think about
>>>> it: If we want to improve gcc toolchain buildspeed with better
>>>> multithreading.
>>>> I think the most sensible would be fixing up gold multithreading and
>>>> enabling
>>>> it by default. We already get most of the benefits of multicore
>>>> architectures
>>>> by running multiple compile jobs in parallel (yes, I know you are
>>>> focusing on
>>>> cases where that for some reason doesn't work, but it is still the
>>>> case in
>>>> most situations). The main bottleneck is linking. The code is even
>>>> already
>>>> there in gold and have been for years, it just haven't been deemed
>>>> ready for
>>>> being enabled by default.
>>>> Is anyone even working on that?
>>>> Best regards
>>>> Allan
>>> Allan,
>>> You would need both depending on the project, some are more compiler
>>> bottle necked and others linker. I mentioned that issue at Cauldron as
>>> the other side would be the linker.
>>> Nick
>> Sorry for the second message Allan but make -j does not scale well
>> beyond 4 or
>> 8 threads and that's considering a 4 core or 8 machine.
> It doesn't? I generally build with -j100, but then also use icecream to
> distribute builds to multiple machines in the office. That probably also makes
> linking times more significant to my case.
> 'Allan

I ran a gcc build on a machine with make -j32 and -j64 that had 64 cores. There was literally only
a 4 minute increase in build speed. Good question through.



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