Re: Raptor Lake / Alder lake on RELENG_13 ?

From: Mike Karels <>
Date: Tue, 07 Feb 2023 14:09:26 UTC
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.