On 7 Feb 2023, at 7:41, mike tancsa wrote:
> On 2/7/2023 8:29 AM, Mike Karels wrote:
>> On 6 Feb 2023, at 16:04, mike tancsa wrote:
>>
>>> Hi All,
>>>
>>> I have seen a couple of commits around these CPUs, but wondering if
>>> anyone is running 13 on these newer hybrid CPUs ? Do the slower cores just
>>> get disabled or are they made use of somehow ?
>>>
>>> ---Mike
>> I have been testing the changes on -current, and they are working fine. I
>> have not tested on 13, but I would expect the same result. The workaround
>> is on 13-stable, but not yet a RELENG branch. Presumably it will be in 13.2
>> when it is branched. If no one else has reported, I will test the 13.2
>> branch. Also, I haven’t heard of tests on Raptor Lake, but I have heard
>> that the behavior should be the same as Alder Lake.
>>
>> The E-cores are not disabled. They are forced to use a less efficient
>> method of page invalidation. They are scheduled as if they were P-cores
>> without threads, but they are less used because of the shared cache among 4
>> cores rather than 2. I have some preliminary scheduler changes that
>> recognize the slower cores, but there are still issues to be dealt with.
>>
> Thank you very much for the detailed update! Apart from some performance
> tweaking, would you say performance overall is pretty good, or will the
> scheduler enhancements need to be made still ?
>
> ---Mike
Performance seems very good to me. As far as I can tell, the E-cores are
slower than P-cores with a single thread, but faster than the second thread on
a P-core. Hopefully scheduler improvements will help more for a workload that
uses fewer than all hardware threads. Software threading could in theory be
handled better by putting threads where they will share cache, but that is not
a simple addition.
Mike
