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Message-Id: <20200809190615.25647-1-dmtrmonakhov@yandex-team.ru>
Date: Sun, 9 Aug 2020 19:06:15 +0000
From: Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
To: linux-kernel@...r.kernel.org
Cc: koct9i@...il.com, Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
Subject: [PATCH] lib/test_lockup.c: add parameters for cond_resched inside loop
call_cond_resched_before=Y call cond_resched with resource before wait
call_cond_resched_after=Y call cond_resched with resource after wait
measure_cond_resched=Y measure maximum cond_resched time inside loop
This simulate situation where process call cond_resched() with lock held.
Example demonstrate priority inversion issue with epbf-program, where
low priority task sheduled out while holding cgroup_mutex for a long
periods of time which blocks others programs with high priority.
CGROUP_MUTEX=$(gawk '$3 == "cgroup_mutex" {print "0x"$1}' /proc/kallsyms)
# Emulate ebpf-application load which can hung inside cgroup_bpf_attach()
nice -20 modprobe lib/test_lockup.ko \
time_nsecs=1000 cooldown_nsecs=100000 iterations=100000 \
lock_mutex_ptr=$CGROUP_MUTEX \
measure_lock_wait=Y call_cond_resched_after=Y &
stress-ng -c $(nproc) --timeout 10s&
time mkdir /sys/fs/cgroup/blkio/a
Signed-off-by: Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
---
lib/test_lockup.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 43 insertions(+), 1 deletion(-)
diff --git a/lib/test_lockup.c b/lib/test_lockup.c
index 0f81252..3e05d6e 100644
--- a/lib/test_lockup.c
+++ b/lib/test_lockup.c
@@ -77,6 +77,18 @@ static bool call_cond_resched;
module_param(call_cond_resched, bool, 0600);
MODULE_PARM_DESC(call_cond_resched, "call cond_resched() between iterations");
+static bool call_cond_resched_before;
+module_param(call_cond_resched_before, bool, 0600);
+MODULE_PARM_DESC(call_cond_resched_before, "call cond_resched() before wait");
+
+static bool call_cond_resched_after;
+module_param(call_cond_resched_after, bool, 0600);
+MODULE_PARM_DESC(call_cond_resched_after, "call cond_resched() after wait");
+
+static bool measure_cond_resched;
+module_param(measure_cond_resched, bool, 0400);
+MODULE_PARM_DESC(measure_cond_resched, "measure cond_resched time");
+
static bool measure_lock_wait;
module_param(measure_lock_wait, bool, 0400);
MODULE_PARM_DESC(measure_lock_wait, "measure lock wait time");
@@ -162,6 +174,7 @@ MODULE_PARM_DESC(lock_sb_umount, "lock file -> sb -> s_umount");
static atomic_t alloc_pages_failed = ATOMIC_INIT(0);
static atomic64_t max_lock_wait = ATOMIC64_INIT(0);
+static atomic64_t max_cond_resched = ATOMIC64_INIT(0);
static struct task_struct *main_task;
static int master_cpu;
@@ -346,6 +359,22 @@ static void test_wait(unsigned int secs, unsigned int nsecs)
}
}
+static void test_cond_resched(void)
+{
+ s64 cur, old_max;
+ s64 start = local_clock();
+
+ cond_resched();
+
+ cur = local_clock() - start;
+ old_max = atomic64_read(&max_cond_resched);
+ do {
+ if (cur < old_max)
+ break;
+ old_max = atomic64_cmpxchg(&max_cond_resched, old_max, cur);
+ } while (old_max != cur);
+}
+
static void test_lockup(bool master)
{
u64 lockup_start = local_clock();
@@ -363,8 +392,14 @@ static void test_lockup(bool master)
if (iowait)
current->in_iowait = 1;
+ if (call_cond_resched_before)
+ test_cond_resched();
+
test_wait(time_secs, time_nsecs);
+ if (call_cond_resched_after)
+ test_cond_resched();
+
if (iowait)
current->in_iowait = 0;
@@ -497,6 +532,7 @@ static int __init test_lockup_init(void)
if ((wait_state != TASK_RUNNING ||
(call_cond_resched && !reacquire_locks) ||
+ call_cond_resched_before || call_cond_resched_after ||
(alloc_pages_nr && gfpflags_allow_blocking(alloc_pages_gfp))) &&
(test_disable_irq || disable_softirq || disable_preempt ||
lock_rcu || lock_spinlock_ptr || lock_rwlock_ptr)) {
@@ -532,7 +568,7 @@ static int __init test_lockup_init(void)
if (test_lock_sb_umount && test_inode)
lock_rwsem_ptr = (unsigned long)&test_inode->i_sb->s_umount;
- pr_notice("START pid=%d time=%u +%u ns cooldown=%u +%u ns iterations=%u state=%s %s%s%s%s%s%s%s%s%s%s%s\n",
+ pr_notice("START pid=%d time=%u +%u ns cooldown=%u +%u ns iterations=%u state=%s %s%s%s%s%s%s%s%s%s%s%s%s%s\n",
main_task->pid, time_secs, time_nsecs,
cooldown_secs, cooldown_nsecs, iterations, state,
all_cpus ? "all_cpus " : "",
@@ -545,6 +581,8 @@ static int __init test_lockup_init(void)
touch_softlockup ? "touch_softlockup " : "",
touch_hardlockup ? "touch_hardlockup " : "",
call_cond_resched ? "call_cond_resched " : "",
+ call_cond_resched_before ? "call_cond_resched_before " : "",
+ call_cond_resched_after ? "call_cond_resched_after " : "",
reacquire_locks ? "reacquire_locks " : "");
if (alloc_pages_nr)
@@ -578,6 +616,10 @@ static int __init test_lockup_init(void)
pr_notice("Maximum lock wait: %lld ns\n",
atomic64_read(&max_lock_wait));
+ if (measure_cond_resched)
+ pr_notice("Maximum cond resched time: %lld ns\n",
+ atomic64_read(&max_cond_resched));
+
if (alloc_pages_nr)
pr_notice("Page allocation failed %u times\n",
atomic_read(&alloc_pages_failed));
--
2.7.4
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