user/sven/linux.git/include/linux/tick.h, branch v4.13.6

cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely

2017-03-23T01:12:14Z

The way the schedutil governor uses the PELT metric causes it to underestimate the CPU utilization in some cases. That can be easily demonstrated by running kernel compilation on a Sandy Bridge Intel processor, running turbostat in parallel with it and looking at the values written to the MSR_IA32_PERF_CTL register. Namely, the expected result would be that when all CPUs were 100% busy, all of them would be requested to run in the maximum P-state, but observation shows that this clearly isn't the case. The CPUs run in the maximum P-state for a while and then are requested to run slower and go back to the maximum P-state after a while again. That causes the actual frequency of the processor to visibly oscillate below the sustainable maximum in a jittery fashion which clearly is not desirable. That has been attributed to CPU utilization metric updates on task migration that cause the total utilization value for the CPU to be reduced by the utilization of the migrated task. If that happens, the schedutil governor may see a CPU utilization reduction and will attempt to reduce the CPU frequency accordingly right away. That may be premature, though, for example if the system is generally busy and there are other runnable tasks waiting to be run on that CPU already. This is unlikely to be an issue on systems where cpufreq policies are shared between multiple CPUs, because in those cases the policy utilization is computed as the maximum of the CPU utilization values over the whole policy and if that turns out to be low, reducing the frequency for the policy most likely is a good idea anyway. On systems with one CPU per policy, however, it may affect performance adversely and even lead to increased energy consumption in some cases. On those systems it may be addressed by taking another utilization metric into consideration, like whether or not the CPU whose frequency is about to be reduced has been idle recently, because if that's not the case, the CPU is likely to be busy in the near future and its frequency should not be reduced. To that end, use the counter of idle calls in the timekeeping code. Namely, make the schedutil governor look at that counter for the current CPU every time before its frequency is about to be reduced. If the counter has not changed since the previous iteration of the governor computations for that CPU, the CPU has been busy for all that time and its frequency should not be decreased, so if the new frequency would be lower than the one set previously, the governor will skip the frequency update. Signed-off-by: Rafael J. Wysocki Acked-by: Peter Zijlstra (Intel) Acked-by: Viresh Kumar Reviewed-by: Joel Fernandes

ktime: Get rid of the union

2016-12-25T16:21:22Z

ktime is a union because the initial implementation stored the time in scalar nanoseconds on 64 bit machine and in a endianess optimized timespec variant for 32bit machines. The Y2038 cleanup removed the timespec variant and switched everything to scalar nanoseconds. The union remained, but become completely pointless. Get rid of the union and just keep ktime_t as simple typedef of type s64. The conversion was done with coccinelle and some manual mopping up. Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra

param: convert some "on"/"off" users to strtobool

2016-03-17T22:09:34Z

This changes several users of manual "on"/"off" parsing to use strtobool. Some side-effects: - these uses will now parse y/n/1/0 meaningfully too - the early_param uses will now bubble up parse errors Signed-off-by: Kees Cook Acked-by: Heiko Carstens Acked-by: Michael Ellerman Cc: Amitkumar Karwar Cc: Andy Shevchenko Cc: Daniel Borkmann Cc: Joe Perches Cc: Kalle Valo Cc: Martin Schwidefsky Cc: Nishant Sarmukadam Cc: Rasmus Villemoes Cc: Steve French Cc: Stephen Rothwell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

posix-cpu-timers: Migrate to use new tick dependency mask model

2016-03-02T15:44:27Z

Instead of providing asynchronous checks for the nohz subsystem to verify posix cpu timers tick dependency, migrate the latter to the new mask. In order to keep track of the running timers and expose the tick dependency accordingly, we must probe the timers queuing and dequeuing on threads and process lists. Unfortunately it implies both task and signal level dependencies. We should be able to further optimize this and merge all that on the task level dependency, at the cost of a bit of complexity and may be overhead. Reviewed-by: Chris Metcalf Cc: Christoph Lameter Cc: Chris Metcalf Cc: Ingo Molnar Cc: Luiz Capitulino Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Cc: Viresh Kumar Signed-off-by: Frederic Weisbecker

perf: Migrate perf to use new tick dependency mask model

2016-03-02T15:43:00Z

Instead of providing asynchronous checks for the nohz subsystem to verify perf event tick dependency, migrate perf to the new mask. Perf needs the tick for two situations: 1) Freq events. We could set the tick dependency when those are installed on a CPU context. But setting a global dependency on top of the global freq events accounting is much easier. If people want that to be optimized, we can still refine that on the per-CPU tick dependency level. This patch dooesn't change the current behaviour anyway. 2) Throttled events: this is a per-cpu dependency. Reviewed-by: Chris Metcalf Cc: Christoph Lameter Cc: Chris Metcalf Cc: Ingo Molnar Cc: Luiz Capitulino Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Cc: Viresh Kumar Signed-off-by: Frederic Weisbecker

nohz: Use enum code for tick stop failure tracing message

2016-03-02T15:42:15Z

It makes nohz tracing more lightweight, standard and easier to parse. Examples: user_loop-2904 [007] d..1 517.701126: tick_stop: success=1 dependency=NONE user_loop-2904 [007] dn.1 518.021181: tick_stop: success=0 dependency=SCHED posix_timers-6142 [007] d..1 1739.027400: tick_stop: success=0 dependency=POSIX_TIMER user_loop-5463 [007] dN.1 1185.931939: tick_stop: success=0 dependency=PERF_EVENTS Suggested-by: Peter Zijlstra Reviewed-by: Chris Metcalf Cc: Christoph Lameter Cc: Chris Metcalf Cc: Ingo Molnar Cc: Luiz Capitulino Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Cc: Viresh Kumar Signed-off-by: Frederic Weisbecker

nohz: New tick dependency mask

2016-03-02T15:41:39Z

The tick dependency is evaluated on every IRQ and context switch. This consists is a batch of checks which determine whether it is safe to stop the tick or not. These checks are often split in many details: posix cpu timers, scheduler, sched clock, perf events.... each of which are made of smaller details: posix cpu timer involves checking process wide timers then thread wide timers. Perf involves checking freq events then more per cpu details. Checking these informations asynchronously every time we update the full dynticks state bring avoidable overhead and a messy layout. Let's introduce instead tick dependency masks: one for system wide dependency (unstable sched clock, freq based perf events), one for CPU wide dependency (sched, throttling perf events), and task/signal level dependencies (posix cpu timers). The subsystems are responsible for setting and clearing their dependency through a set of APIs that will take care of concurrent dependency mask modifications and kick targets to restart the relevant CPU tick whenever needed. This new dependency engine stays beside the old one until all subsystems having a tick dependency are converted to it. Suggested-by: Thomas Gleixner Suggested-by: Peter Zijlstra Reviewed-by: Chris Metcalf Cc: Christoph Lameter Cc: Chris Metcalf Cc: Ingo Molnar Cc: Luiz Capitulino Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Cc: Viresh Kumar Signed-off-by: Frederic Weisbecker

time: nohz: Expose tick_nohz_enabled

2016-01-15T21:34:39Z

The cpuidle subsystem needs it. Signed-off-by: Jean Delvare Reviewed-by: Thomas Gleixner Signed-off-by: Rafael J. Wysocki

nohz: Affine unpinned timers to housekeepers

2015-09-02T08:33:22Z

The problem addressed in this patch is about affining unpinned timers. Adaptive or Full Dynticks CPUs are currently disturbed by unnecessary jitter due to firing of such timers on them. This patch will affine timers to online CPUs which are not full dynticks in NOHZ_FULL configured systems. It should not introduce overhead in nohz full off case due to static keys. Signed-off-by: Vatika Harlalka Signed-off-by: Frederic Weisbecker Reviewed-by: Preeti U Murthy Acked-by: Thomas Gleixner Cc: Chris Metcalf Cc: Christoph Lameter Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1441119060-2230-2-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar

nohz: Remove useless argument on tick_nohz_task_switch()

2015-07-29T13:45:01Z

Leftover from early code. Cc: Christoph Lameter Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Preeti U Murthy Cc: Rik van Riel Cc: Thomas Gleixner Cc: Viresh Kumar Signed-off-by: Frederic Weisbecker