Intel Adding Linux Idle Driver Support For Alder Lake

While Intel Alder Lake has been out for roughly a half-year now and has been working out well on Linux particularly with v5.16+ kernels, the "intel_idle" driver for CPU idle time management hasn't supported these latest Intel desktop/mobile processors but now there is that support on the way for possible power-savings benefits.

Zhang Rui of Intel on Friday sent out a patch adding Alder Lake support to the intel_idle Linux driver. This is similar to the Intel Idle driver just recently adding Xeon Sapphire Rapids support.

The intel_idle driver works with MWAIT-supported Intel CPUs and aims to provide more power efficient Linux usage. We'll see though the impact for Alder Lake as so far the Linux CPU power numbers aren't vastly different from what we see under Windows. With the Alder Lake support patch only being posted now, it won't be mainlined until at least Linux 5.19.

Like with the Sapphire Rapids intel_idle work previously talked about, the C1 and C1E power states are now mutually exclusive with only one of those states can be enabled at a time. But with this Alder Lake support, C1E is being preferred over C1 -- unlike with Sapphire Rapids where C1 is preferred due to lower latency in exiting the state as is important for server performance characteristics. So with Alder Lake by default C1E will be preferred for greater power-savings albeit with slightly higher latency. But as with Linux and open-source in general, that C1 and C1E preference is configurable with the kernel.

The patch also carries custom c-state tables tuned for both Alder Lake mobile and Alder Lake desktop processors. We'll see if this Intel Idle driver support for Alder Lake makes any meaningful difference once this belated code is mainlined.