On Thu, Aug 18, 2022 at 03:03:33PM +0200, Jan Beulich wrote: > From: Artem Bityutskiy <[email protected]> > > On Sapphire Rapids Xeon (SPR) the C1 and C1E states are basically mutually > exclusive - only one of them can be enabled. By default, 'intel_idle' driver > enables C1 and disables C1E. However, some users prefer to use C1E instead of > C1, because it saves more energy. > > This patch adds a new module parameter ('preferred_cstates') for enabling C1E > and disabling C1. Here is the idea behind it. > > 1. This option has effect only for "mutually exclusive" C-states like C1 and > C1E on SPR. > 2. It does not have any effect on independent C-states, which do not require > other C-states to be disabled (most states on most platforms as of today). > 3. For mutually exclusive C-states, the 'intel_idle' driver always has a > reasonable default, such as enabling C1 on SPR by default. On other > platforms, the default may be different. > 4. Users can override the default using the 'preferred_cstates' parameter. > 5. The parameter accepts the preferred C-states bit-mask, similarly to the > existing 'states_off' parameter. > 6. This parameter is not limited to C1/C1E, and leaves room for supporting > other mutually exclusive C-states, if they come in the future. > > Today 'intel_idle' can only be compiled-in, which means that on SPR, in order > to disable C1 and enable C1E, users should boot with the following kernel > argument: intel_idle.preferred_cstates=4 > > Signed-off-by: Artem Bityutskiy <[email protected]> > Signed-off-by: Rafael J. Wysocki <[email protected]> > Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git > da0e58c038e6 > > Enable C1E (if requested) not only on the BSP's socket / package. Alter > command line option to fit our model, and extend it to also accept > string form arguments. > > Signed-off-by: Jan Beulich <[email protected]>
Acked-by: Roger Pau Monné <[email protected]> With the indentation fixes. Thanks, Roger.
