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authorSuren Baghdasaryan <surenb@google.com>2019-05-14 15:40:56 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-05-14 19:52:47 -0700
commit33b2d6302abc4ccea1d9b3f095e2e27b02ca264e (patch)
treefd8e1273ddd7b2cac58ab8cc0d7e05e6597d7b60 /kernel/sched
parent136ac591f047fc356072343eb85687f7c6ea191d (diff)
psi: introduce state_mask to represent stalled psi states
Patch series "psi: pressure stall monitors", v6. This is a respin of: https://lwn.net/ml/linux-kernel/20190308184311.144521-1-surenb%40google.com/ Android is adopting psi to detect and remedy memory pressure that results in stuttering and decreased responsiveness on mobile devices. Psi gives us the stall information, but because we're dealing with latencies in the millisecond range, periodically reading the pressure files to detect stalls in a timely fashion is not feasible. Psi also doesn't aggregate its averages at a high-enough frequency right now. This patch series extends the psi interface such that users can configure sensitive latency thresholds and use poll() and friends to be notified when these are breached. As high-frequency aggregation is costly, it implements an aggregation method that is optimized for fast, short-interval averaging, and makes the aggregation frequency adaptive, such that high-frequency updates only happen while monitored stall events are actively occurring. With these patches applied, Android can monitor for, and ward off, mounting memory shortages before they cause problems for the user. For example, using memory stall monitors in userspace low memory killer daemon (lmkd) we can detect mounting pressure and kill less important processes before device becomes visibly sluggish. In our memory stress testing psi memory monitors produce roughly 10x less false positives compared to vmpressure signals. Having ability to specify multiple triggers for the same psi metric allows other parts of Android framework to monitor memory state of the device and act accordingly. The new interface is straight-forward. The user opens one of the pressure files for writing and writes a trigger description into the file descriptor that defines the stall state - some or full, and the maximum stall time over a given window of time. E.g.: /* Signal when stall time exceeds 100ms of a 1s window */ char trigger[] = "full 100000 1000000" fd = open("/proc/pressure/memory") write(fd, trigger, sizeof(trigger)) while (poll() >= 0) { ... }; close(fd); When the monitored stall state is entered, psi adapts its aggregation frequency according to what the configured time window requires in order to emit event signals in a timely fashion. Once the stalling subsides, aggregation reverts back to normal. The trigger is associated with the open file descriptor. To stop monitoring, the user only needs to close the file descriptor and the trigger is discarded. Patches 1-6 prepare the psi code for polling support. Patch 7 implements the adaptive polling logic, the pressure growth detection optimized for short intervals, and hooks up write() and poll() on the pressure files. The patches were developed in collaboration with Johannes Weiner. This patch (of 7): The psi monitoring patches will need to determine the same states as record_times(). To avoid calculating them twice, maintain a state mask that can be consulted cheaply. Do this in a separate patch to keep the churn in the main feature patch at a minimum. This adds 4-byte state_mask member into psi_group_cpu struct which results in its first cacheline-aligned part becoming 52 bytes long. Add explicit values to enumeration element counters that affect psi_group_cpu struct size. Link: http://lkml.kernel.org/r/20190124211518.244221-4-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Dennis Zhou <dennis@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Li Zefan <lizefan@huawei.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/psi.c29
1 files changed, 19 insertions, 10 deletions
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 0e97ca9306ef..22c1505ad290 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -213,17 +213,17 @@ static bool test_state(unsigned int *tasks, enum psi_states state)
static void get_recent_times(struct psi_group *group, int cpu, u32 *times)
{
struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
- unsigned int tasks[NR_PSI_TASK_COUNTS];
u64 now, state_start;
+ enum psi_states s;
unsigned int seq;
- int s;
+ u32 state_mask;
/* Snapshot a coherent view of the CPU state */
do {
seq = read_seqcount_begin(&groupc->seq);
now = cpu_clock(cpu);
memcpy(times, groupc->times, sizeof(groupc->times));
- memcpy(tasks, groupc->tasks, sizeof(groupc->tasks));
+ state_mask = groupc->state_mask;
state_start = groupc->state_start;
} while (read_seqcount_retry(&groupc->seq, seq));
@@ -239,7 +239,7 @@ static void get_recent_times(struct psi_group *group, int cpu, u32 *times)
* (u32) and our reported pressure close to what's
* actually happening.
*/
- if (test_state(tasks, s))
+ if (state_mask & (1 << s))
times[s] += now - state_start;
delta = times[s] - groupc->times_prev[s];
@@ -407,15 +407,15 @@ static void record_times(struct psi_group_cpu *groupc, int cpu,
delta = now - groupc->state_start;
groupc->state_start = now;
- if (test_state(groupc->tasks, PSI_IO_SOME)) {
+ if (groupc->state_mask & (1 << PSI_IO_SOME)) {
groupc->times[PSI_IO_SOME] += delta;
- if (test_state(groupc->tasks, PSI_IO_FULL))
+ if (groupc->state_mask & (1 << PSI_IO_FULL))
groupc->times[PSI_IO_FULL] += delta;
}
- if (test_state(groupc->tasks, PSI_MEM_SOME)) {
+ if (groupc->state_mask & (1 << PSI_MEM_SOME)) {
groupc->times[PSI_MEM_SOME] += delta;
- if (test_state(groupc->tasks, PSI_MEM_FULL))
+ if (groupc->state_mask & (1 << PSI_MEM_FULL))
groupc->times[PSI_MEM_FULL] += delta;
else if (memstall_tick) {
u32 sample;
@@ -436,10 +436,10 @@ static void record_times(struct psi_group_cpu *groupc, int cpu,
}
}
- if (test_state(groupc->tasks, PSI_CPU_SOME))
+ if (groupc->state_mask & (1 << PSI_CPU_SOME))
groupc->times[PSI_CPU_SOME] += delta;
- if (test_state(groupc->tasks, PSI_NONIDLE))
+ if (groupc->state_mask & (1 << PSI_NONIDLE))
groupc->times[PSI_NONIDLE] += delta;
}
@@ -448,6 +448,8 @@ static void psi_group_change(struct psi_group *group, int cpu,
{
struct psi_group_cpu *groupc;
unsigned int t, m;
+ enum psi_states s;
+ u32 state_mask = 0;
groupc = per_cpu_ptr(group->pcpu, cpu);
@@ -480,6 +482,13 @@ static void psi_group_change(struct psi_group *group, int cpu,
if (set & (1 << t))
groupc->tasks[t]++;
+ /* Calculate state mask representing active states */
+ for (s = 0; s < NR_PSI_STATES; s++) {
+ if (test_state(groupc->tasks, s))
+ state_mask |= (1 << s);
+ }
+ groupc->state_mask = state_mask;
+
write_seqcount_end(&groupc->seq);
}