On Tuesday, August 25, 2015 08:03:06 PM Ashwin Chaugule wrote: > On 25 August 2015 at 20:24, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > > On Wednesday, August 05, 2015 09:40:23 AM Ashwin Chaugule wrote: > >> CPPC: > >> ==== > >> > >> CPPC (Collaborative Processor Performance Control) is a new way to control CPU > >> performance using an abstract continous scale as against a discretized P-state scale > >> which is tied to CPU frequency only. It is defined in the ACPI 5.0+ spec. In brief, > >> the basic operation involves: > >> - OS makes a CPU performance request. (Can provide min and max tolerable bounds) > >> > >> - Platform (such as BMC) is free to optimize request within requested bounds depending > >> on power/thermal budgets etc. > >> > >> - Platform conveys its decision back to OS > >> > >> The communication between OS and platform occurs through another medium called (PCC) > >> Platform communication Channel. This is a generic mailbox like mechanism which includes > >> doorbell semantics to indicate register updates. See drivers/mailbox/pcc.c > >> > >> This patchset introduces a CPPC based CPUFreq driver that works with existing governors > >> such as ondemand. The CPPC table parsing and the CPPC communication semantics are > >> abstracted into separate files to allow future CPPC based drivers to implement their > >> own governors if required. > >> > >> Initial patchsets included an adaptation of the PID governor from intel_pstate.c. However > >> recent experiments led to extensive modifications of the algorithm to calculate CPU > >> busyness. Until it is verified that these changes are worthwhile, the existing governors > >> should provide for a good enough starting point for ARM64 servers. > >> > >> Finer details about the PCC and CPPC spec are available in the latest ACPI 5.1 > >> specification.[2] > >> > >> Testing: > >> ======= > >> > >> This was tested on an SBSA compatible ARMv8 server with CPPCv2 > >> firmware running on a remote processor. I verified that each CPUs > >> performance limits were detected and that new performance requests > >> were made by the on-demand governor proportional to the load on each > >> CPU. I also verified that using the acpi_processor driver correctly > >> maps the physical CPU ids to logical CPU ids, which helps in picking > >> up the proper _CPC details from a processor object, in the case where > >> CPU physical ids may not be contiguous. > >> > >> Changes since V7: > >> - Simplied new kconfig options for PSS and idle. > >> - Separated patch to enable acpi processor on ARM64. > >> - Removed redundant kconfig cross deps on PCC. > >> - Decoupled processor_perflib from new PSS kconfig option. > >> > >> Changes since V6: > >> - Separated PSS and CST from ACPI processor driver in two patches. > >> - Made new Kconfig symbols auto selectable from Arch Kconfigs. > >> > >> Changes since V5: > >> - Checkpatch cleanups. > >> - Change pss_init to pss_perf_init. Rec by Srinivas Pandruvada. > >> - Explicit comment explaining why postcore_initcall to pcc mailbox. > >> - Fold acpi_processor_syscore_init/exit into CONFIG_ACPI_CST. > >> - Added patch with dummy functions used by ACPI_HOTPLUG_CPU. > >> > >> Changes since V4: > >> - Misc cleanups. Addressed feedback from Rafael. > >> - Made acpi_processor.c independent of C-states, P-states and others. > >> - Per CPU scanning for _CPC is now made from acpi_processor.c > >> - Added new Kconfig options for legacy C states and P states to enable future > >> support for newer alternatives as defined in the ACPI spec 6.0. > >> > >> Changes since V3: > >> - Split CPPC backend methods into separate files. > >> - Add frontend driver which plugs into existing CPUfreq governors. > >> - Simplify PCC driver by moving communication space mapping and read/write > >> into client drivers. > >> > >> Changes since V2: > >> - Select driver if !X86, since intel_pstate will use HWP extensions instead. > >> - Added more comments. > >> - Added Freq domain awareness and PSD parsing. > >> > >> Changes since V1: > >> - Create a new driver based on Dirks suggestion. > >> - Fold in CPPC backend hooks into main driver. > >> > >> Changes since V0: [1] > >> - Split intel_pstate.c into a generic PID governor and platform specific backend. > >> - Add CPPC accessors as PID backend. > >> > >> [1] - http://lwn.net/Articles/608715/ > >> [2] - http://www.uefi.org/sites/default/files/resources/ACPI_5_1release.pdf > >> [3] - https://patches.linaro.org/40705/ > >> > >> > >> Ashwin Chaugule (9): > >> PCC: Initialize PCC Mailbox earlier at boot > >> ACPI: Split out ACPI PSS from ACPI Processor driver > >> ACPI: Decouple ACPI idle and ACPI processor drivers > >> ACPI: Introduce CPU performance controls using CPPC > >> CPPC: Add a CPUFreq driver for use with CPPC > >> ACPI: Add weak routines for ACPI CPU Hotplug > >> CPPC: Probe for CPPC tables for each ACPI Processor object > >> PCC: Disable compilation by default > >> ACPI: Allow selection of the ACPI processor driver for ARM64 > > > > I've queued up [1-3/9] for 4.3, but I still have a couple of questions/comments > > regarding [4/9] and the rest of the series (I'll respond to the patch messages > > with those). > > Thanks! Would you mind taking [8/9] too? It just defaults PCC to disabled. OK, I'll do that. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
