Merge branch 'akpm' (patches from Andrew)

spikes which wouldn't necessarily make a dent in the time averages,

or to average trends over custom time frames.

Monitoring for pressure thresholds

==================================

Users can register triggers and use poll() to be woken up when resource

pressure exceeds certain thresholds.

A trigger describes the maximum cumulative stall time over a specific

time window, e.g. 100ms of total stall time within any 500ms window to

generate a wakeup event.

To register a trigger user has to open psi interface file under

/proc/pressure/ representing the resource to be monitored and write the

desired threshold and time window. The open file descriptor should be

used to wait for trigger events using select(), poll() or epoll().

The following format is used:

<some|full> <stall amount in us> <time window in us>

For example writing "some 150000 1000000" into /proc/pressure/memory

would add 150ms threshold for partial memory stall measured within

1sec time window. Writing "full 50000 1000000" into /proc/pressure/io

would add 50ms threshold for full io stall measured within 1sec time window.

Triggers can be set on more than one psi metric and more than one trigger

for the same psi metric can be specified. However for each trigger a separate

file descriptor is required to be able to poll it separately from others,

therefore for each trigger a separate open() syscall should be made even

when opening the same psi interface file.

Monitors activate only when system enters stall state for the monitored

psi metric and deactivates upon exit from the stall state. While system is

in the stall state psi signal growth is monitored at a rate of 10 times per

tracking window.

The kernel accepts window sizes ranging from 500ms to 10s, therefore min

monitoring update interval is 50ms and max is 1s. Min limit is set to

prevent overly frequent polling. Max limit is chosen as a high enough number

after which monitors are most likely not needed and psi averages can be used

instead.

When activated, psi monitor stays active for at least the duration of one

tracking window to avoid repeated activations/deactivations when system is

bouncing in and out of the stall state.

Notifications to the userspace are rate-limited to one per tracking window.

The trigger will de-register when the file descriptor used to define the

trigger  is closed.

Userspace monitor usage example

===============================

#include <errno.h>

#include <fcntl.h>

#include <stdio.h>

#include <poll.h>

#include <string.h>

#include <unistd.h>

/*

 * Monitor memory partial stall with 1s tracking window size

 * and 150ms threshold.

 */

int main() {

	const char trig[] = "some 150000 1000000";

	struct pollfd fds;

	int n;

	fds.fd = open("/proc/pressure/memory", O_RDWR | O_NONBLOCK);

	if (fds.fd < 0) {

		printf("/proc/pressure/memory open error: %s\n",

			strerror(errno));

		return 1;

	}

	fds.events = POLLPRI;

	if (write(fds.fd, trig, strlen(trig) + 1) < 0) {

		printf("/proc/pressure/memory write error: %s\n",

			strerror(errno));

		return 1;

	}

	printf("waiting for events...\n");

	while (1) {

		n = poll(&fds, 1, -1);

		if (n < 0) {

			printf("poll error: %s\n", strerror(errno));

			return 1;

		}

		if (fds.revents & POLLERR) {

			printf("got POLLERR, event source is gone\n");

			return 0;

		}

		if (fds.revents & POLLPRI) {

			printf("event triggered!\n");

		} else {

			printf("unknown event received: 0x%x\n", fds.revents);

			return 1;

		}

	}

	return 0;

}

Cgroup2 interface

=================

into cgroups. Each subdirectory in the cgroupfs mountpoint contains

cpu.pressure, memory.pressure, and io.pressure files; the format is

the same as the /proc/pressure/ files.

Per-cgroup psi monitors can be specified and used the same way as

system-wide ones.

	ip=		[IP_PNP]

			See Documentation/filesystems/nfs/nfsroot.txt.

	ipcmni_extend	[KNL] Extend the maximum number of unique System V

			IPC identifiers from 32,768 to 16,777,216.

	irqaffinity=	[SMP] Set the default irq affinity mask

			The argument is a cpu list, as described above.

			This will also cause panics on machine check exceptions.

			Useful together with panic=30 to trigger a reboot.

	page_alloc.shuffle=

			[KNL] Boolean flag to control whether the page allocator

			should randomize its free lists. The randomization may

			be automatically enabled if the kernel detects it is

			running on a platform with a direct-mapped memory-side

			cache, and this parameter can be used to

			override/disable that behavior. The state of the flag

			can be read from sysfs at:

			/sys/module/page_alloc/parameters/shuffle.

	page_owner=	[KNL] Boot-time page_owner enabling option.

			Storage of the information about who allocated

			each page is disabled in default. With this switch,

				[[,]s[mp]#### \

				[[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \

				[[,]f[orce]

			Where reboot_mode is one of warm (soft) or cold (hard) or gpio,

			Where reboot_mode is one of warm (soft) or cold (hard) or gpio

					(prefix with 'panic_' to set mode for panic

					reboot only),

			      reboot_type is one of bios, acpi, kbd, triple, efi, or pci,

			      reboot_force is either force or not specified,

			      reboot_cpu is s[mp]#### with #### being the processor

.. kernel-doc:: include/linux/math64.h

   :internal:

.. kernel-doc:: lib/div64.c

.. kernel-doc:: lib/math/div64.c

   :functions: div_s64_rem div64_u64_rem div64_u64 div64_s64

.. kernel-doc:: lib/gcd.c

.. kernel-doc:: lib/math/gcd.c

   :export:

UUID/GUID

        CONFIG_DEBUG_FS=y

        CONFIG_GCOV_KERNEL=y

select the gcc's gcov format, default is autodetect based on gcc version::

        CONFIG_GCOV_FORMAT_AUTODETECT=y

and to get coverage data for the entire kernel::

        CONFIG_GCOV_PROFILE_ALL=y

      [user@build] gcov -o /tmp/coverage/tmp/out/init main.c

Note on compilers

-----------------

GCC and LLVM gcov tools are not necessarily compatible. Use gcov_ to work with

GCC-generated .gcno and .gcda files, and use llvm-cov_ for Clang.

.. _gcov: http://gcc.gnu.org/onlinedocs/gcc/Gcov.html

.. _llvm-cov: https://llvm.org/docs/CommandGuide/llvm-cov.html

Build differences between GCC and Clang gcov are handled by Kconfig. It

automatically selects the appropriate gcov format depending on the detected

toolchain.

Troubleshooting

---------------

- compatible: should be "pps-gpio"

- gpios: one PPS GPIO in the format described by ../gpio/gpio.txt

Additional required properties for the PPS ECHO functionality:

- echo-gpios: one PPS ECHO GPIO in the format described by ../gpio/gpio.txt

- echo-active-ms: duration in ms of the active portion of the echo pulse

Optional properties:

- assert-falling-edge: when present, assert is indicated by a falling edge

                       (instead of by a rising edge)

		gpios = <&gpio1 26 GPIO_ACTIVE_HIGH>;

		assert-falling-edge;

		echo-gpios = <&gpio1 27 GPIO_ACTIVE_HIGH>;

		echo-active-ms = <100>;

		compatible = "pps-gpio";

	};