From afa3701c0e45ecb9e4d160048ca4e353c7489948 Mon Sep 17 00:00:00 2001 From: Tiffany Yang Date: Thu, 21 Aug 2025 18:37:52 -0700 Subject: [PATCH] cgroup: cgroup.stat.local time accounting MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit There isn't yet a clear way to identify a set of "lost" time that everyone (or at least a wider group of users) cares about. However, users can perform some delay accounting by iterating over components of interest. This patch allows cgroup v2 freezing time to be one of those components. Track the cumulative time that each v2 cgroup spends freezing and expose it to userland via a new local stat file in cgroupfs. Thank you to Michal, who provided the ASCII art in the updated documentation. To access this value: $ mkdir /sys/fs/cgroup/test $ cat /sys/fs/cgroup/test/cgroup.stat.local freeze_time_total 0 Ensure consistent freeze time reads with freeze_seq, a per-cgroup sequence counter. Writes are serialized using the css_set_lock. Signed-off-by: Tiffany Yang Cc: Tejun Heo Cc: Michal Koutný Signed-off-by: Tejun Heo --- Documentation/admin-guide/cgroup-v2.rst | 18 ++++++++++++++++ include/linux/cgroup-defs.h | 17 +++++++++++++++ kernel/cgroup/cgroup.c | 28 +++++++++++++++++++++++++ kernel/cgroup/freezer.c | 16 ++++++++++---- 4 files changed, 75 insertions(+), 4 deletions(-) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index d9d3cc7df348..9a3a909ee40b 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1001,6 +1001,24 @@ All cgroup core files are prefixed with "cgroup." Total number of dying cgroup subsystems (e.g. memory cgroup) at and beneath the current cgroup. + cgroup.stat.local + A read-only flat-keyed file which exists in non-root cgroups. + The following entry is defined: + + frozen_usec + Cumulative time that this cgroup has spent between freezing and + thawing, regardless of whether by self or ancestor groups. + NB: (not) reaching "frozen" state is not accounted here. + + Using the following ASCII representation of a cgroup's freezer + state, :: + + 1 _____ + frozen 0 __/ \__ + ab cd + + the duration being measured is the span between a and c. + cgroup.freeze A read-write single value file which exists on non-root cgroups. Allowed values are "0" and "1". The default is "0". diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 6b93a64115fe..539c64eeef38 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -433,6 +433,23 @@ struct cgroup_freezer_state { * frozen, SIGSTOPped, and PTRACEd. */ int nr_frozen_tasks; + + /* Freeze time data consistency protection */ + seqcount_t freeze_seq; + + /* + * Most recent time the cgroup was requested to freeze. + * Accesses guarded by freeze_seq counter. Writes serialized + * by css_set_lock. + */ + u64 freeze_start_nsec; + + /* + * Total duration the cgroup has spent freezing. + * Accesses guarded by freeze_seq counter. Writes serialized + * by css_set_lock. + */ + u64 frozen_nsec; }; struct cgroup { diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 312c6a8b55bb..ab096b884bbc 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3763,6 +3763,27 @@ static int cgroup_stat_show(struct seq_file *seq, void *v) return 0; } +static int cgroup_core_local_stat_show(struct seq_file *seq, void *v) +{ + struct cgroup *cgrp = seq_css(seq)->cgroup; + unsigned int sequence; + u64 freeze_time; + + do { + sequence = read_seqcount_begin(&cgrp->freezer.freeze_seq); + freeze_time = cgrp->freezer.frozen_nsec; + /* Add in current freezer interval if the cgroup is freezing. */ + if (test_bit(CGRP_FREEZE, &cgrp->flags)) + freeze_time += (ktime_get_ns() - + cgrp->freezer.freeze_start_nsec); + } while (read_seqcount_retry(&cgrp->freezer.freeze_seq, sequence)); + + seq_printf(seq, "frozen_usec %llu\n", + (unsigned long long) freeze_time / NSEC_PER_USEC); + + return 0; +} + #ifdef CONFIG_CGROUP_SCHED /** * cgroup_tryget_css - try to get a cgroup's css for the specified subsystem @@ -5354,6 +5375,11 @@ static struct cftype cgroup_base_files[] = { .name = "cgroup.stat", .seq_show = cgroup_stat_show, }, + { + .name = "cgroup.stat.local", + .flags = CFTYPE_NOT_ON_ROOT, + .seq_show = cgroup_core_local_stat_show, + }, { .name = "cgroup.freeze", .flags = CFTYPE_NOT_ON_ROOT, @@ -5763,6 +5789,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent, const char *name, * if the parent has to be frozen, the child has too. */ cgrp->freezer.e_freeze = parent->freezer.e_freeze; + seqcount_init(&cgrp->freezer.freeze_seq); if (cgrp->freezer.e_freeze) { /* * Set the CGRP_FREEZE flag, so when a process will be @@ -5771,6 +5798,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent, const char *name, * consider it frozen immediately. */ set_bit(CGRP_FREEZE, &cgrp->flags); + cgrp->freezer.freeze_start_nsec = ktime_get_ns(); set_bit(CGRP_FROZEN, &cgrp->flags); } diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c index bf1690a167dd..6c18854bff34 100644 --- a/kernel/cgroup/freezer.c +++ b/kernel/cgroup/freezer.c @@ -171,7 +171,7 @@ static void cgroup_freeze_task(struct task_struct *task, bool freeze) /* * Freeze or unfreeze all tasks in the given cgroup. */ -static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze) +static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze, u64 ts_nsec) { struct css_task_iter it; struct task_struct *task; @@ -179,10 +179,16 @@ static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze) lockdep_assert_held(&cgroup_mutex); spin_lock_irq(&css_set_lock); - if (freeze) + write_seqcount_begin(&cgrp->freezer.freeze_seq); + if (freeze) { set_bit(CGRP_FREEZE, &cgrp->flags); - else + cgrp->freezer.freeze_start_nsec = ts_nsec; + } else { clear_bit(CGRP_FREEZE, &cgrp->flags); + cgrp->freezer.frozen_nsec += (ts_nsec - + cgrp->freezer.freeze_start_nsec); + } + write_seqcount_end(&cgrp->freezer.freeze_seq); spin_unlock_irq(&css_set_lock); if (freeze) @@ -260,6 +266,7 @@ void cgroup_freeze(struct cgroup *cgrp, bool freeze) struct cgroup *parent; struct cgroup *dsct; bool applied = false; + u64 ts_nsec; bool old_e; lockdep_assert_held(&cgroup_mutex); @@ -271,6 +278,7 @@ void cgroup_freeze(struct cgroup *cgrp, bool freeze) return; cgrp->freezer.freeze = freeze; + ts_nsec = ktime_get_ns(); /* * Propagate changes downwards the cgroup tree. @@ -298,7 +306,7 @@ void cgroup_freeze(struct cgroup *cgrp, bool freeze) /* * Do change actual state: freeze or unfreeze. */ - cgroup_do_freeze(dsct, freeze); + cgroup_do_freeze(dsct, freeze, ts_nsec); applied = true; } -- 2.51.0