linux.git/include/linux/psi.h, branch v6.1

sched/psi: Per-cgroup PSI accounting disable/re-enable interface

2022-09-09T09:08:33+00:00

PSI accounts stalls for each cgroup separately and aggregates it
at each level of the hierarchy. This may cause non-negligible overhead
for some workloads when under deep level of the hierarchy.

commit 3958e2d0c34e ("cgroup: make per-cgroup pressure stall tracking configurable")
make PSI to skip per-cgroup stall accounting, only account system-wide
to avoid this each level overhead.

But for our use case, we also want leaf cgroup PSI stats accounted for
userspace adjustment on that cgroup, apart from only system-wide adjustment.

So this patch introduce a per-cgroup PSI accounting disable/re-enable
interface "cgroup.pressure", which is a read-write single value file that
allowed values are "0" and "1", the defaults is "1" so per-cgroup
PSI stats is enabled by default.

Implementation details:

It should be relatively straight-forward to disable and re-enable
state aggregation, time tracking, averaging on a per-cgroup level,
if we can live with losing history from while it was disabled.
I.e. the avgs will restart from 0, total= will have gaps.

But it's hard or complex to stop/restart groupc->tasks[] updates,
which is not implemented in this patch. So we always update
groupc->tasks[] and PSI_ONCPU bit in psi_group_change() even when
the cgroup PSI stats is disabled.

Suggested-by: Johannes Weiner 
Suggested-by: Tejun Heo 
Signed-off-by: Chengming Zhou 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Johannes Weiner 
Link: https://lkml.kernel.org/r/20220907090332.2078-1-zhouchengming@bytedance.com

sched/psi: Consolidate cgroup_psi()

2022-09-09T09:08:33+00:00

cgroup_psi() can't return psi_group for root cgroup, so we have many
open code "psi = cgroup_ino(cgrp) == 1 ? &psi_system : cgrp->psi".

This patch move cgroup_psi() definition to , in which
we can return psi_system for root cgroup, so can handle all cgroups.

Signed-off-by: Chengming Zhou 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Johannes Weiner 
Link: https://lore.kernel.org/r/20220825164111.29534-9-zhouchengming@bytedance.com

sched/psi: Move private helpers to sched/stats.h

2022-09-09T09:08:31+00:00

This patch move psi_task_change/psi_task_switch declarations out of
PSI public header, since they are only needed for implementing the
PSI stats tracking in sched/stats.h

psi_task_switch is obvious, psi_task_change can't be public helper
since it doesn't check psi_disabled static key. And there is no
any user now, so put it in sched/stats.h too.

Signed-off-by: Chengming Zhou 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Johannes Weiner 
Link: https://lore.kernel.org/r/20220825164111.29534-5-zhouchengming@bytedance.com

sched/psi: Remove unused parameter nbytes of psi_trigger_create()

2022-08-15T22:35:25+00:00

psi_trigger_create()'s 'nbytes' parameter is not used, so we can remove it.

Signed-off-by: Hao Jia 
Reviewed-by: Ingo Molnar 
Acked-by: Johannes Weiner 
Signed-off-by: Tejun Heo

headers/prep: Fix header to build standalone:

2022-03-21T10:13:49+00:00

Add the  dependency to , because
cgroup_move_task() will dereference 'struct css_set'.

( Only older toolchains are affected, due to variations in
  the implementation of rcu_assign_pointer() et al. )

Cc: Peter Zijlstra 
Cc: Linus Torvalds 
Reported-by: Sachin Sant 
Reported-by: Andrew Morton 
Reported-by: Borislav Petkov 
Signed-off-by: Ingo Molnar

psi: fix "no previous prototype" warnings when CONFIG_CGROUPS=n

2022-01-30T07:56:58+00:00

When CONFIG_CGROUPS is disabled psi code generates the following
warnings:

  kernel/sched/psi.c:1112:21: warning: no previous prototype for 'psi_trigger_create' [-Wmissing-prototypes]
      1112 | struct psi_trigger *psi_trigger_create(struct psi_group *group,
           |                     ^~~~~~~~~~~~~~~~~~
  kernel/sched/psi.c:1182:6: warning: no previous prototype for 'psi_trigger_destroy' [-Wmissing-prototypes]
      1182 | void psi_trigger_destroy(struct psi_trigger *t)
           |      ^~~~~~~~~~~~~~~~~~~
  kernel/sched/psi.c:1249:10: warning: no previous prototype for 'psi_trigger_poll' [-Wmissing-prototypes]
      1249 | __poll_t psi_trigger_poll(void **trigger_ptr,
           |          ^~~~~~~~~~~~~~~~

Change the declarations of these functions in the header to provide the
prototypes even when they are unused.

Link: https://lkml.kernel.org/r/20220119223940.787748-2-surenb@google.com
Fixes: 0e94682b73bf ("psi: introduce psi monitor")
Signed-off-by: Suren Baghdasaryan 
Reported-by: kernel test robot 
Acked-by: Johannes Weiner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

psi: Fix uaf issue when psi trigger is destroyed while being polled

2022-01-18T11:09:57+00:00

With write operation on psi files replacing old trigger with a new one,
the lifetime of its waitqueue is totally arbitrary. Overwriting an
existing trigger causes its waitqueue to be freed and pending poll()
will stumble on trigger->event_wait which was destroyed.
Fix this by disallowing to redefine an existing psi trigger. If a write
operation is used on a file descriptor with an already existing psi
trigger, the operation will fail with EBUSY error.
Also bypass a check for psi_disabled in the psi_trigger_destroy as the
flag can be flipped after the trigger is created, leading to a memory
leak.

Fixes: 0e94682b73bf ("psi: introduce psi monitor")
Reported-by: syzbot+cdb5dd11c97cc532efad@syzkaller.appspotmail.com
Suggested-by: Linus Torvalds 
Analyzed-by: Eric Biggers 
Signed-off-by: Suren Baghdasaryan 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Eric Biggers 
Acked-by: Johannes Weiner 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220111232309.1786347-1-surenb@google.com

psi: Add a missing SPDX license header

2021-11-17T13:48:59+00:00

Add the missing SPDX license header to
include/linux/psi.h
include/linux/psi_types.h
kernel/sched/psi.c

Signed-off-by: Liu Xinpeng 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Johannes Weiner 
Link: https://lore.kernel.org/r/1635133586-84611-2-git-send-email-liuxp11@chinatelecom.cn

psi: Use ONCPU state tracking machinery to detect reclaim

2021-03-06T11:40:22+00:00

Move the reclaim detection from the timer tick to the task state
tracking machinery using the recently added ONCPU state. And we
also add task psi_flags changes checking in the psi_task_switch()
optimization to update the parents properly.

In terms of performance and cost, this ONCPU task state tracking
is not cheaper than previous timer tick in aggregate. But the code is
simpler and shorter this way, so it's a maintainability win. And
Johannes did some testing with perf bench, the performace and cost
changes would be acceptable for real workloads.

Thanks to Johannes Weiner for pointing out the psi_task_switch()
optimization things and the clearer changelog.

Co-developed-by: Muchun Song 
Signed-off-by: Muchun Song 
Signed-off-by: Chengming Zhou 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Acked-by: Johannes Weiner 
Link: https://lkml.kernel.org/r/20210303034659.91735-3-zhouchengming@bytedance.com

psi: Optimize switching tasks inside shared cgroups

2020-03-20T12:06:19+00:00

When switching tasks running on a CPU, the psi state of a cgroup
containing both of these tasks does not change. Right now, we don't
exploit that, and can perform many unnecessary state changes in nested
hierarchies, especially when most activity comes from one leaf cgroup.

This patch implements an optimization where we only update cgroups
whose state actually changes during a task switch. These are all
cgroups that contain one task but not the other, up to the first
shared ancestor. When both tasks are in the same group, we don't need
to update anything at all.

We can identify the first shared ancestor by walking the groups of the
incoming task until we see TSK_ONCPU set on the local CPU; that's the
first group that also contains the outgoing task.

The new psi_task_switch() is similar to psi_task_change(). To allow
code reuse, move the task flag maintenance code into a new function
and the poll/avg worker wakeups into the shared psi_group_change().

Suggested-by: Peter Zijlstra 
Signed-off-by: Johannes Weiner 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20200316191333.115523-3-hannes@cmpxchg.org