[RFC PATCH 2/3] x86/resctrl: Move the task's threads to the group automatically

[Babu Moger <babu.moger@xxxxxxx>]

Some micro benchmarks run multiple threads when started. Monitoring
(or controlling) the benchmark using the task id is bit tricky. Users
need to track all the threads and assign them individually to monitor
or control. For example:
  $stream_lowOverhead -codeAlg 13 -nRep 100000 -cores 0 1 2 3 -memMB 32
  -alignKB 8192 -aPadB 0 -bPadB 0 -cPadB 0 -testMask 1

  $pidof stream_lowOverhead
  6793

This benchmark actually runs multiple threads underneath on the cores
listed above. It can be seen with the command:
  $ps -T -p 6793
   PID   SPID TTY          TIME CMD
  6793   6793 pts/2    00:00:00 stream_lowOverh
  6793   6802 pts/2    00:01:25 stream_lowOverh
  6793   6803 pts/2    00:01:25 stream_lowOverh
  6793   6804 pts/2    00:01:25 stream_lowOverh
  6793   6805 pts/2    00:01:25 stream_lowOverh

Users need to assign these threads individually to the resctrl group for
monitoring or controlling.

  $echo 6793 > /sys/fs/restrl/clos1/tasks
  $echo 6802 > /sys/fs/restrl/clos1/tasks
  $echo 6803 > /sys/fs/restrl/clos1/tasks
  $echo 6804 > /sys/fs/restrl/clos1/tasks
  $echo 6805 > /sys/fs/restrl/clos1/tasks

That is not easy when dealing with numerous threads.

Detect the task's threads automatically and assign them to the resctrl
group when parent task is assigned. For example:
  $echo 6793 > /sys/fs/restrl/clos1/tasks

All the threads will be assigned to the group automatically.
  $cat /sys/fs/restrl/clos1/tasks
  6793
  6793
  6802
  6803
  6804
  6805

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 344607853f4c..0d71ed22cfa9 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -685,6 +685,7 @@ static int rdtgroup_move_task(pid_t pid, struct rdtgroup *rdtgrp,
 static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
 				    char *buf, size_t nbytes, loff_t off)
 {
+	struct task_struct *task, *thread;
 	struct rdtgroup *rdtgrp;
 	char *pid_str;
 	int ret = 0;
@@ -723,7 +724,13 @@ static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
 		goto exit;
 	}
 
-	ret = rdtgroup_move_task(pid, rdtgrp, of);
+	task = find_task_by_vpid(pid);
+	thread = task;
+	do {
+		ret = rdtgroup_move_task(thread->pid, rdtgrp, of);
+		if (ret)
+			goto exit;
+	} while_each_thread(task, thread);
 
 	goto next;