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Giovanni Gherdovich 298c6f99bf x86, sched: Add support for frequency invariance on ATOM
The scheduler needs the ratio freq_curr/freq_max for frequency-invariant
accounting. On all ATOM CPUs prior to Goldmont, set freq_max to the 1-core
turbo ratio.

We intended to perform tests validating that this patch doesn't regress in
terms of energy efficiency, given that this is the primary concern on Atom
processors. Alas, we found out that turbostat doesn't support reading RAPL
interfaces on our test machine (Airmont), and we don't have external equipment
to measure power consumption; all we have is the performance results of the
benchmarks we ran.

Test machine:

Platform    : Dell Wyse 3040 Thin Client[1]
CPU Model   : Intel Atom x5-Z8350 (aka Cherry Trail, aka Airmont)
Fam/Mod/Ste : 6:76:4
Topology    : 1 socket, 4 cores / 4 threads
Memory      : 2G
Storage     : onboard flash, XFS filesystem

[1] https://www.dell.com/en-us/work/shop/wyse-endpoints-and-software/wyse-3040-thin-client/spd/wyse-3040-thin-client

Base frequency and available turbo levels (MHz):

    Min Operating Freq   266 |***
    Low Freq Mode        800 |********
    Base Freq           2400 |************************
    4 Cores             2800 |****************************
    3 Cores             2800 |****************************
    2 Cores             3200 |********************************
    1 Core              3200 |********************************

Tested kernels:

Baseline      : v5.4-rc1,              intel_pstate passive,  schedutil
Comparison #1 : v5.4-rc1,              intel_pstate active ,  powersave
Comparison #2 : v5.4-rc1, this patch,  intel_pstate passive,  schedutil

tbench, hackbench and kernbench performed the same under all three kernels;
dbench ran faster with intel_pstate/powersave and the git unit tests were a
lot faster with intel_pstate/powersave and invariant schedutil wrt the
baseline. Not that any of this is terrbily interesting anyway, one doesn't buy
an Atom system to go fast. Power consumption regressions aren't expected but
we lack the equipment to make that measurement. Turbostat seems to think that
reading RAPL on this machine isn't a good idea and we're trusting that
decision.

comparison ratio of performance with baseline; 1.00 means neutral,
lower is better:

                      I_PSTATE      FREQ-INV
    ----------------------------------------
    dbench                0.90             ~
    kernbench             0.98          0.97
    gitsource             0.63          0.43

Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lkml.kernel.org/r/20200122151617.531-6-ggherdovich@suse.cz
2020-01-28 21:37:05 +01:00
Documentation Fixes for 5.5: 2019-12-22 10:59:06 -08:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch x86, sched: Add support for frequency invariance on ATOM 2020-01-28 21:37:05 +01:00
block block: fix memleak when __blk_rq_map_user_iov() is failed 2019-12-20 11:52:01 -07:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto tpmdd fixes for Linux v5.5-rc3 2019-12-18 17:17:36 -08:00
drivers Linux 5.5-rc3 2019-12-25 10:41:37 +01:00
fs Linux 5.5-rc3 2019-12-25 10:41:37 +01:00
include timers/nohz: Update NOHZ load in remote tick 2020-01-28 21:36:44 +01:00
init early init: fix error handling when opening /dev/console 2019-12-17 13:10:11 -08:00
ipc treewide: Use sizeof_field() macro 2019-12-09 10:36:44 -08:00
kernel x86, sched: Add support for frequency invariance 2020-01-28 21:36:59 +01:00
lib Linux 5.5-rc3 2019-12-25 10:41:37 +01:00
mm Linux 5.5-rc3 2019-12-25 10:41:37 +01:00
net Linux 5.5-rc3 2019-12-25 10:41:37 +01:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-12-22 09:54:33 -08:00
scripts Kbuild fixes for v5.5 2019-12-21 10:49:47 -08:00
security tpmdd fixes for Linux v5.5-rc3 2019-12-18 17:17:36 -08:00
sound sound fixes for 5.5-rc3 2019-12-18 08:54:15 -08:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-12-22 09:54:33 -08:00
usr kbuild: fix 'No such file or directory' warning when cleaning 2019-12-09 10:08:21 +09:00
virt PPC KVM fix for 5.5 2019-12-22 13:18:15 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
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.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
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COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Linux 5.4-rc4 2019-10-29 04:43:29 -06:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS PPC: 2019-12-22 10:26:59 -08:00
Makefile Linux 5.5-rc3 2019-12-22 17:02:23 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.