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authorMichal Koutný <mkoutny@suse.com>2019-10-04 12:57:40 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2022-09-15 12:04:54 +0200
commit059516952cc9cc303b3bd0c558abef193a736fe2 (patch)
treeca5717cc840dd7b0b1a2e4c768fe726a664fba1f /kernel
parentd0e7be0dc9f2c6b6f14755748a85c1697c0ebbbf (diff)
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cgroup: Optimize single thread migration
[ Upstream commit 9a3284fad42f66bb43629c6716709ff791aaa457 ] There are reports of users who use thread migrations between cgroups and they report performance drop after d59cfc09c32a ("sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem"). The effect is pronounced on machines with more CPUs. The migration is affected by forking noise happening in the background, after the mentioned commit a migrating thread must wait for all (forking) processes on the system, not only of its threadgroup. There are several places that need to synchronize with migration: a) do_exit, b) de_thread, c) copy_process, d) cgroup_update_dfl_csses, e) parallel migration (cgroup_{proc,thread}s_write). In the case of self-migrating thread, we relax the synchronization on cgroup_threadgroup_rwsem to avoid the cost of waiting. d) and e) are excluded with cgroup_mutex, c) does not matter in case of single thread migration and the executing thread cannot exec(2) or exit(2) while it is writing into cgroup.threads. In case of do_exit because of signal delivery, we either exit before the migration or finish the migration (of not yet PF_EXITING thread) and die afterwards. This patch handles only the case of self-migration by writing "0" into cgroup.threads. For simplicity, we always take cgroup_threadgroup_rwsem with numeric PIDs. This change improves migration dependent workload performance similar to per-signal_struct state. Signed-off-by: Michal Koutný <mkoutny@suse.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cgroup/cgroup-internal.h5
-rw-r--r--kernel/cgroup/cgroup-v1.c5
-rw-r--r--kernel/cgroup/cgroup.c39
3 files changed, 36 insertions, 13 deletions
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 236f290224aa..8dfb2526b3aa 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -250,9 +250,10 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup,
int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
bool threadgroup);
-struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
+struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup,
+ bool *locked)
__acquires(&cgroup_threadgroup_rwsem);
-void cgroup_procs_write_finish(struct task_struct *task)
+void cgroup_procs_write_finish(struct task_struct *task, bool locked)
__releases(&cgroup_threadgroup_rwsem);
void cgroup_lock_and_drain_offline(struct cgroup *cgrp);
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 117d70098cd4..aa7577b189e9 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -498,12 +498,13 @@ static ssize_t __cgroup1_procs_write(struct kernfs_open_file *of,
struct task_struct *task;
const struct cred *cred, *tcred;
ssize_t ret;
+ bool locked;
cgrp = cgroup_kn_lock_live(of->kn, false);
if (!cgrp)
return -ENODEV;
- task = cgroup_procs_write_start(buf, threadgroup);
+ task = cgroup_procs_write_start(buf, threadgroup, &locked);
ret = PTR_ERR_OR_ZERO(task);
if (ret)
goto out_unlock;
@@ -526,7 +527,7 @@ static ssize_t __cgroup1_procs_write(struct kernfs_open_file *of,
ret = cgroup_attach_task(cgrp, task, threadgroup);
out_finish:
- cgroup_procs_write_finish(task);
+ cgroup_procs_write_finish(task, locked);
out_unlock:
cgroup_kn_unlock(of->kn);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 23f0db2900e4..bc9ee9a18c1e 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2856,7 +2856,8 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
return ret;
}
-struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
+struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup,
+ bool *locked)
__acquires(&cgroup_threadgroup_rwsem)
{
struct task_struct *tsk;
@@ -2865,7 +2866,21 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
return ERR_PTR(-EINVAL);
- percpu_down_write(&cgroup_threadgroup_rwsem);
+ /*
+ * If we migrate a single thread, we don't care about threadgroup
+ * stability. If the thread is `current`, it won't exit(2) under our
+ * hands or change PID through exec(2). We exclude
+ * cgroup_update_dfl_csses and other cgroup_{proc,thread}s_write
+ * callers by cgroup_mutex.
+ * Therefore, we can skip the global lock.
+ */
+ lockdep_assert_held(&cgroup_mutex);
+ if (pid || threadgroup) {
+ percpu_down_write(&cgroup_threadgroup_rwsem);
+ *locked = true;
+ } else {
+ *locked = false;
+ }
rcu_read_lock();
if (pid) {
@@ -2896,13 +2911,16 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
goto out_unlock_rcu;
out_unlock_threadgroup:
- percpu_up_write(&cgroup_threadgroup_rwsem);
+ if (*locked) {
+ percpu_up_write(&cgroup_threadgroup_rwsem);
+ *locked = false;
+ }
out_unlock_rcu:
rcu_read_unlock();
return tsk;
}
-void cgroup_procs_write_finish(struct task_struct *task)
+void cgroup_procs_write_finish(struct task_struct *task, bool locked)
__releases(&cgroup_threadgroup_rwsem)
{
struct cgroup_subsys *ss;
@@ -2911,7 +2929,8 @@ void cgroup_procs_write_finish(struct task_struct *task)
/* release reference from cgroup_procs_write_start() */
put_task_struct(task);
- percpu_up_write(&cgroup_threadgroup_rwsem);
+ if (locked)
+ percpu_up_write(&cgroup_threadgroup_rwsem);
for_each_subsys(ss, ssid)
if (ss->post_attach)
ss->post_attach();
@@ -4830,12 +4849,13 @@ static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
struct task_struct *task;
const struct cred *saved_cred;
ssize_t ret;
+ bool locked;
dst_cgrp = cgroup_kn_lock_live(of->kn, false);
if (!dst_cgrp)
return -ENODEV;
- task = cgroup_procs_write_start(buf, true);
+ task = cgroup_procs_write_start(buf, true, &locked);
ret = PTR_ERR_OR_ZERO(task);
if (ret)
goto out_unlock;
@@ -4861,7 +4881,7 @@ static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
ret = cgroup_attach_task(dst_cgrp, task, true);
out_finish:
- cgroup_procs_write_finish(task);
+ cgroup_procs_write_finish(task, locked);
out_unlock:
cgroup_kn_unlock(of->kn);
@@ -4881,6 +4901,7 @@ static ssize_t cgroup_threads_write(struct kernfs_open_file *of,
struct task_struct *task;
const struct cred *saved_cred;
ssize_t ret;
+ bool locked;
buf = strstrip(buf);
@@ -4888,7 +4909,7 @@ static ssize_t cgroup_threads_write(struct kernfs_open_file *of,
if (!dst_cgrp)
return -ENODEV;
- task = cgroup_procs_write_start(buf, false);
+ task = cgroup_procs_write_start(buf, false, &locked);
ret = PTR_ERR_OR_ZERO(task);
if (ret)
goto out_unlock;
@@ -4919,7 +4940,7 @@ static ssize_t cgroup_threads_write(struct kernfs_open_file *of,
ret = cgroup_attach_task(dst_cgrp, task, false);
out_finish:
- cgroup_procs_write_finish(task);
+ cgroup_procs_write_finish(task, locked);
out_unlock:
cgroup_kn_unlock(of->kn);
generated by cgit v1.2.3 (git 2.25.1) at 2025-03-14 05:25:07 +0000