Date: Fri, 4 Mar 2022 09:03:06 +0000 From: Bob Bishop <rb@gid.co.uk> To: mike@karels.net Cc: "freebsd-arch@freebsd.org" <freebsd-arch@FreeBSD.org> Subject: Re: support for asymmetric CPUs Message-ID: <310CBE30-6E24-4F17-9E52-76E067E8BF52@gid.co.uk> In-Reply-To: <202203040139.2241d20M045464@mail.karels.net> References: <202203040139.2241d20M045464@mail.karels.net>
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Hi, > On 4 Mar 2022, at 01:39, Mike Karels <mike@karels.net> wrote: >=20 > Replying to several messages, including my own: >=20 > Although several people mentioned energy efficiency, that is not my > immediate goal. At least with the Alder Lake CPUs, I suspect that the > difference in energy use between low load on P-cores and E-cores is > small. These are not especially energy-efficient chips; the i7-12700K > is rated at a base power of 125 W, with a peak of 190 W. Instead, I = am > more interested in system throughput and sensible placement decisions > using fairly simple algorithms. I plan to experiment with starting > most processes on E-cores, and promoting to P-cores as soon as they > start using much CPU time. This should reserve the P-cores for the > processes that most need them, and keep the processes with lower > utilization from interrupting them and disturbing caches. In any = case, > I'm hoping that simple algorithms can beat random placement. Naively, > I hope that similar strategies would also lower power consumption for > varying workloads with mixed core types, although not as much as > algorithms that were more sensitive to efficiency of different types > of workload on the different cores. I haven't decided yet whether to > consider threaded processes differently; the E-cores are supposedly = better > for threaded processes. >=20 > I also don't know if/when I'll experiment with Intel's Hardware = Feedback > Interface; it will obviously depend on availability of documentation = or > example code. In theory HFI could yield quicker placement decisions. Section 14.6 of this for a starter: = https://www.intel.com/content/dam/develop/public/us/en/documents/253669-sd= m-vol-3b.pdf > Any additional input welcomed... >=20 > Mike >=20 -- Bob Bishop rb@gid.co.uk
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