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Subject[PATCH][v6] x86/resctrl: Add task resctrl information display
Date
Monitoring tools that want to find out which resctrl control
and monitor groups a task belongs to must currently read
the "tasks" file in every group until they locate the process
ID.

Add an additional file /proc/{pid}/cpu_resctrl to provide this
information.

The output is as followed, for example:

1) ""
Resctrl is not available.

2) "/"
Task is part of the root group, task is not associated to
any monitor group.

3) "/mon_groups/mon0"
Task is part of the root group and monitor group mon0.

4) "/group0"
Task is part of resctrl control group group0, task is not
associated to any monitor group.

5) "/group0/mon_groups/mon1"
Task is part of resctrl control group group0 and monitor
group mon1.

Tested-by: Jinshi Chen <jinshi.chen@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Reinette Chatre <reinette.chatre@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
v1: Initial version reviewed by Reinette Chatre,
Fenghua Yu and Tony Luck.

v2: According to Boris's suggestion,
reduce indentation level in proc_resctrl_show().
Create the include/linux/resctrl.h header and
declare proc_resctrl_show() in this file, so
that other architectures would probably use it
in the future. Different architectures should
implement architectural specific proc_resctrl_show()
accordingly.

v3: According to Boris's suggestion,
Return empty string if the resctrl filesystem has
not been mounted.
Rename the config from CPU_RESCTRL to PROC_CPU_RESCTRL
to better represent its usage. Move PROC_CPU_RESCTRL
from arch/Kconfig to fs/proc/Kconfig.
And let PROC_CPU_RESCTRL to be depended on PROC_FS.

v4: According to Thomas's suggestion, changed the output
from multiple lines to one single line.

v5: According to Alexey's feedback, removed the header file
proc_fs.h in resctrl.h, and changed seq_puts() to
seq_putc() for simplicity.

v6: According to Chris Down's suggestion,
1. rename:
/proc/{pid}/resctrl to /proc/{pid}/cpu_resctrl
to better reflect its meaning.
2. change the description in comments:
"control group" to "resctrl control group"
as the former is confusing for cgroup users.
---
arch/x86/Kconfig | 1 +
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 79 ++++++++++++++++++++++++++
fs/proc/Kconfig | 4 ++
fs/proc/base.c | 7 +++
include/linux/resctrl.h | 14 +++++
5 files changed, 105 insertions(+)
create mode 100644 include/linux/resctrl.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5e8949953660..6e17a68c7d77 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -456,6 +456,7 @@ config X86_CPU_RESCTRL
bool "x86 CPU resource control support"
depends on X86 && (CPU_SUP_INTEL || CPU_SUP_AMD)
select KERNFS
+ select PROC_CPU_RESCTRL if PROC_FS
help
Enable x86 CPU resource control support.

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 2e3b06d6bbc6..dcbf62d6b689 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -725,6 +725,85 @@ static int rdtgroup_tasks_show(struct kernfs_open_file *of,
return ret;
}

+#ifdef CONFIG_PROC_CPU_RESCTRL
+
+/*
+ * A task can only be part of one resctrl
+ * control group and of one monitor
+ * group which is associated to that resctrl
+ * control group.
+ * So one line is simple and clear enough:
+ *
+ * 1) ""
+ * resctrl is not available.
+ *
+ * 2) "/"
+ * Task is part of the root group, and it is
+ * not associated to any monitor group.
+ *
+ * 3) "/mon_groups/mon0"
+ * Task is part of the root group and monitor
+ * group mon0.
+ *
+ * 4) "/group0"
+ * Task is part of resctrl control group group0,
+ * and it is not associated to any monitor group.
+ *
+ * 5) "/group0/mon_groups/mon1"
+ * Task is part of resctrl control group group0 and monitor
+ * group mon1.
+ */
+int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns,
+ struct pid *pid, struct task_struct *tsk)
+{
+ struct rdtgroup *rdtg;
+ int ret = 0;
+
+ mutex_lock(&rdtgroup_mutex);
+
+ /* Return empty if resctrl has not been mounted. */
+ if (!static_branch_unlikely(&rdt_enable_key))
+ goto unlock;
+
+ list_for_each_entry(rdtg, &rdt_all_groups, rdtgroup_list) {
+ struct rdtgroup *crg;
+
+ /*
+ * Task information is only relevant for shareable
+ * and exclusive groups.
+ */
+ if (rdtg->mode != RDT_MODE_SHAREABLE &&
+ rdtg->mode != RDT_MODE_EXCLUSIVE)
+ continue;
+
+ if (rdtg->closid != tsk->closid)
+ continue;
+
+ seq_printf(s, "/%s", rdtg->kn->name);
+ list_for_each_entry(crg, &rdtg->mon.crdtgrp_list,
+ mon.crdtgrp_list) {
+ if (tsk->rmid != crg->mon.rmid)
+ continue;
+ seq_printf(s, "%smon_groups/%s",
+ rdtg == &rdtgroup_default ? "" : "/",
+ crg->kn->name);
+ break;
+ }
+ seq_putc(s, '\n');
+ goto unlock;
+ }
+ /*
+ * The above search should succeed. Otherwise return
+ * with an error.
+ */
+ ret = -ENOENT;
+unlock:
+ mutex_unlock(&rdtgroup_mutex);
+
+ return ret;
+}
+#endif
+
static int rdt_last_cmd_status_show(struct kernfs_open_file *of,
struct seq_file *seq, void *v)
{
diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
index 733881a6387b..27ef84d99f59 100644
--- a/fs/proc/Kconfig
+++ b/fs/proc/Kconfig
@@ -103,3 +103,7 @@ config PROC_CHILDREN
config PROC_PID_ARCH_STATUS
def_bool n
depends on PROC_FS
+
+config PROC_CPU_RESCTRL
+ def_bool n
+ depends on PROC_FS
diff --git a/fs/proc/base.c b/fs/proc/base.c
index ebea9501afb8..32c9ff154667 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -94,6 +94,7 @@
#include <linux/sched/debug.h>
#include <linux/sched/stat.h>
#include <linux/posix-timers.h>
+#include <linux/resctrl.h>
#include <trace/events/oom.h>
#include "internal.h"
#include "fd.h"
@@ -3060,6 +3061,9 @@ static const struct pid_entry tgid_base_stuff[] = {
#endif
#ifdef CONFIG_CGROUPS
ONE("cgroup", S_IRUGO, proc_cgroup_show),
+#endif
+#ifdef CONFIG_PROC_CPU_RESCTRL
+ ONE("cpu_resctrl", S_IRUGO, proc_resctrl_show),
#endif
ONE("oom_score", S_IRUGO, proc_oom_score),
REG("oom_adj", S_IRUGO|S_IWUSR, proc_oom_adj_operations),
@@ -3460,6 +3464,9 @@ static const struct pid_entry tid_base_stuff[] = {
#endif
#ifdef CONFIG_CGROUPS
ONE("cgroup", S_IRUGO, proc_cgroup_show),
+#endif
+#ifdef CONFIG_PROC_CPU_RESCTRL
+ ONE("cpu_resctrl", S_IRUGO, proc_resctrl_show),
#endif
ONE("oom_score", S_IRUGO, proc_oom_score),
REG("oom_adj", S_IRUGO|S_IWUSR, proc_oom_adj_operations),
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
new file mode 100644
index 000000000000..daf5cf64c6a6
--- /dev/null
+++ b/include/linux/resctrl.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _RESCTRL_H
+#define _RESCTRL_H
+
+#ifdef CONFIG_PROC_CPU_RESCTRL
+
+int proc_resctrl_show(struct seq_file *m,
+ struct pid_namespace *ns,
+ struct pid *pid,
+ struct task_struct *tsk);
+
+#endif
+
+#endif /* _RESCTRL_H */
--
2.17.1
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