[PATCH 8/9] sched/psi: add kernel cmdline parameter psi_inner_cgroup

Chengming Zhou
2022-07-21T04:06:18Z

PSI accounts stalls for each cgroup separately and aggregates it
at each level of the hierarchy. This may case 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.

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

So this patch add kernel cmdline parameter "psi_inner_cgroup" to control
whether or not to account for inner cgroups, which is default to true
for compatibility.

Performance test on Intel Xeon Platinum with 3 levels of cgroup:

1. default (psi_inner_cgroup=true)

$ perf bench sched all
# Running sched/messaging benchmark...
# 20 sender and receiver processes per group
# 10 groups == 400 processes run

Total time: 0.032 [sec]

# Running sched/pipe benchmark...
# Executed 1000000 pipe operations between two processes

Total time: 7.758 [sec]

7.758354 usecs/op
128893 ops/sec

2. psi_inner_cgroup=false

$ perf bench sched all
# Running sched/messaging benchmark...
# 20 sender and receiver processes per group
# 10 groups == 400 processes run

Total time: 0.032 [sec]

# Running sched/pipe benchmark...
# Executed 1000000 pipe operations between two processes

Total time: 7.309 [sec]

7.309436 usecs/op
136809 ops/sec

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
kernel/sched/psi.c | 11 ++++++++++-
2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 8090130b544b..6beef5b8bc36 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4419,6 +4419,12 @@
tracking.
Format: <bool>

+ psi_inner_cgroup=
+ [KNL] Enable or disable pressure stall information
+ tracking for the inner cgroups.
+ Format: <bool>
+ default: enabled
+
psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
probe for; one of (bare|imps|exps|lifebook|any).
psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 2228cbf3bdd3..8d76920f47b3 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -147,12 +147,21 @@ static bool psi_enable;
#else
static bool psi_enable = true;
#endif
+
+static bool psi_inner_cgroup __read_mostly = true;
+
static int __init setup_psi(char *str)
{
return kstrtobool(str, &psi_enable) == 0;
}
__setup("psi=", setup_psi);

+static int __init setup_psi_inner_cgroup(char *str)
+{
+ return kstrtobool(str, &psi_inner_cgroup) == 0;
+}
+__setup("psi_inner_cgroup=", setup_psi_inner_cgroup);
+
/* Running averages - we need to be higher-res than loadavg */
#define PSI_FREQ (2*HZ+1) /* 2 sec intervals */
#define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */
@@ -958,7 +967,7 @@ int psi_cgroup_alloc(struct cgroup *cgroup)
group_init(&cgroup->psi);

parent = cgroup_parent(cgroup);
- if (parent && cgroup_parent(parent))
+ if (parent && cgroup_parent(parent) && psi_inner_cgroup)
cgroup->psi.parent = cgroup_psi(parent);
else
cgroup->psi.parent = &psi_system;
--
2.36.1