path: root/Documentation/cpu-hotplug.txt
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authorLinus Torvalds <torvalds@linux-foundation.org>2013-07-03 21:35:40 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2013-07-03 21:35:40 (GMT)
commitf991fae5c6d42dfc5029150b05a78cf3f6c18cc9 (patch)
treed140deb437bde0631778b4984eeb72c1f4ee0c1d /Documentation/cpu-hotplug.txt
parentd4141531f63a29bb2a980092b6f2828c385e6edd (diff)
parent2c843bd92ec276ecb68504b3b5ffa7066183f032 (diff)
Merge tag 'pm+acpi-3.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
Pull power management and ACPI updates from Rafael Wysocki: "This time the total number of ACPI commits is slightly greater than the number of cpufreq commits, but Viresh Kumar (who works on cpufreq) remains the most active patch submitter. To me, the most significant change is the addition of offline/online device operations to the driver core (with the Greg's blessing) and the related modifications of the ACPI core hotplug code. Next are the freezer updates from Colin Cross that should make the freezing of tasks a bit less heavy weight. We also have a couple of regression fixes, a number of fixes for issues that have not been identified as regressions, two new drivers and a bunch of cleanups all over. Highlights: - Hotplug changes to support graceful hot-removal failures. It sometimes is necessary to fail device hot-removal operations gracefully if they cannot be carried out completely. For example, if memory from a memory module being hot-removed has been allocated for the kernel's own use and cannot be moved elsewhere, it's desirable to fail the hot-removal operation in a graceful way rather than to crash the kernel, but currenty a success or a kernel crash are the only possible outcomes of an attempted memory hot-removal. Needless to say, that is not a very attractive alternative and it had to be addressed. However, in order to make it work for memory, I first had to make it work for CPUs and for this purpose I needed to modify the ACPI processor driver. It's been split into two parts, a resident one handling the low-level initialization/cleanup and a modular one playing the actual driver's role (but it binds to the CPU system device objects rather than to the ACPI device objects representing processors). That's been sort of like a live brain surgery on a patient who's riding a bike. So this is a little scary, but since we found and fixed a couple of regressions it caused to happen during the early linux-next testing (a month ago), nobody has complained. As a bonus we remove some duplicated ACPI hotplug code, because the ACPI-based CPU hotplug is now going to use the common ACPI hotplug code. - Lighter weight freezing of tasks. These changes from Colin Cross and Mandeep Singh Baines are targeted at making the freezing of tasks a bit less heavy weight operation. They reduce the number of tasks woken up every time during the freezing, by using the observation that the freezer simply doesn't need to wake up some of them and wait for them all to call refrigerator(). The time needed for the freezer to decide to report a failure is reduced too. Also reintroduced is the check causing a lockdep warining to trigger when try_to_freeze() is called with locks held (which is generally unsafe and shouldn't happen). - cpufreq updates First off, a commit from Srivatsa S Bhat fixes a resume regression introduced during the 3.10 cycle causing some cpufreq sysfs attributes to return wrong values to user space after resume. The fix is kind of fresh, but also it's pretty obvious once Srivatsa has identified the root cause. Second, we have a new freqdomain_cpus sysfs attribute for the acpi-cpufreq driver to provide information previously available via related_cpus. From Lan Tianyu. Finally, we fix a number of issues, mostly related to the CPUFREQ_POSTCHANGE notifier and cpufreq Kconfig options and clean up some code. The majority of changes from Viresh Kumar with bits from Jacob Shin, Heiko Stübner, Xiaoguang Chen, Ezequiel Garcia, Arnd Bergmann, and Tang Yuantian. - ACPICA update A usual bunch of updates from the ACPICA upstream. During the 3.4 cycle we introduced support for ACPI 5 extended sleep registers, but they are only supposed to be used if the HW-reduced mode bit is set in the FADT flags and the code attempted to use them without checking that bit. That caused suspend/resume regressions to happen on some systems. Fix from Lv Zheng causes those registers to be used only if the HW-reduced mode bit is set. Apart from this some other ACPICA bugs are fixed and code cleanups are made by Bob Moore, Tomasz Nowicki, Lv Zheng, Chao Guan, and Zhang Rui. - cpuidle updates New driver for Xilinx Zynq processors is added by Michal Simek. Multidriver support simplification, addition of some missing kerneldoc comments and Kconfig-related fixes come from Daniel Lezcano. - ACPI power management updates Changes to make suspend/resume work correctly in Xen guests from Konrad Rzeszutek Wilk, sparse warning fix from Fengguang Wu and cleanups and fixes of the ACPI device power state selection routine. - ACPI documentation updates Some previously missing pieces of ACPI documentation are added by Lv Zheng and Aaron Lu (hopefully, that will help people to uderstand how the ACPI subsystem works) and one outdated doc is updated by Hanjun Guo. - Assorted ACPI updates We finally nailed down the IA-64 issue that was the reason for reverting commit 9f29ab11ddbf ("ACPI / scan: do not match drivers against objects having scan handlers"), so we can fix it and move the ACPI scan handler check added to the ACPI video driver back to the core. A mechanism for adding CMOS RTC address space handlers is introduced by Lan Tianyu to allow some EC-related breakage to be fixed on some systems. A spec-compliant implementation of acpi_os_get_timer() is added by Mika Westerberg. The evaluation of _STA is added to do_acpi_find_child() to avoid situations in which a pointer to a disabled device object is returned instead of an enabled one with the same _ADR value. From Jeff Wu. Intel BayTrail PCH (Platform Controller Hub) support is added to the ACPI driver for Intel Low-Power Subsystems (LPSS) and that driver is modified to work around a couple of known BIOS issues. Changes from Mika Westerberg and Heikki Krogerus. The EC driver is fixed by Vasiliy Kulikov to use get_user() and put_user() instead of dereferencing user space pointers blindly. Code cleanups are made by Bjorn Helgaas, Nicholas Mazzuca and Toshi Kani. - Assorted power management updates The "runtime idle" helper routine is changed to take the return values of the callbacks executed by it into account and to call rpm_suspend() if they return 0, which allows us to reduce the overall code bloat a bit (by dropping some code that's not necessary any more after that modification). The runtime PM documentation is updated by Alan Stern (to reflect the "runtime idle" behavior change). New trace points for PM QoS are added by Sahara (<keun-o.park@windriver.com>). PM QoS documentation is updated by Lan Tianyu. Code cleanups are made and minor issues are addressed by Bernie Thompson, Bjorn Helgaas, Julius Werner, and Shuah Khan. - devfreq updates New driver for the Exynos5-bus device from Abhilash Kesavan. Minor cleanups, fixes and MAINTAINERS update from MyungJoo Ham, Abhilash Kesavan, Paul Bolle, Rajagopal Venkat, and Wei Yongjun. - OMAP power management updates Adaptive Voltage Scaling (AVS) SmartReflex voltage control driver updates from Andrii Tseglytskyi and Nishanth Menon." * tag 'pm+acpi-3.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm: (162 commits) cpufreq: Fix cpufreq regression after suspend/resume ACPI / PM: Fix possible NULL pointer deref in acpi_pm_device_sleep_state() PM / Sleep: Warn about system time after resume with pm_trace cpufreq: don't leave stale policy pointer in cdbs->cur_policy acpi-cpufreq: Add new sysfs attribute freqdomain_cpus cpufreq: make sure frequency transitions are serialized ACPI: implement acpi_os_get_timer() according the spec ACPI / EC: Add HP Folio 13 to ec_dmi_table in order to skip DSDT scan ACPI: Add CMOS RTC Operation Region handler support ACPI / processor: Drop unused variable from processor_perflib.c cpufreq: tegra: call CPUFREQ_POSTCHANGE notfier in error cases cpufreq: s3c64xx: call CPUFREQ_POSTCHANGE notfier in error cases cpufreq: omap: call CPUFREQ_POSTCHANGE notfier in error cases cpufreq: imx6q: call CPUFREQ_POSTCHANGE notfier in error cases cpufreq: exynos: call CPUFREQ_POSTCHANGE notfier in error cases cpufreq: dbx500: call CPUFREQ_POSTCHANGE notfier in error cases cpufreq: davinci: call CPUFREQ_POSTCHANGE notfier in error cases cpufreq: arm-big-little: call CPUFREQ_POSTCHANGE notfier in error cases cpufreq: powernow-k8: call CPUFREQ_POSTCHANGE notfier in error cases cpufreq: pcc: call CPUFREQ_POSTCHANGE notfier in error cases ...
Diffstat (limited to 'Documentation/cpu-hotplug.txt')
1 files changed, 4 insertions, 2 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index 0efd1b9..edd4b4d 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -370,8 +370,10 @@ A: There is no clear spec defined way from ACPI that can give us that
CPUs in MADT as hotpluggable CPUS. In the case there are no disabled CPUS
we assume 1/2 the number of CPUs currently present can be hotplugged.
- Caveat: Today's ACPI MADT can only provide 256 entries since the apicid field
- in MADT is only 8 bits.
+ Caveat: ACPI MADT can only provide 256 entries in systems with only ACPI 2.0c
+ or earlier ACPI version supported, because the apicid field in MADT is only
+ 8 bits. From ACPI 3.0, this limitation was removed since the apicid field
+ was extended to 32 bits with x2APIC introduced.
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