delayacct: Default disabled

Assuming this stuff isn't actually used much; disable it by default
and avoid allocating and tracking the task_delay_info structure.

taskstats is changed to still report the regular sched and sched_info
and only skip the missing task_delay_info fields instead of not
reporting anything.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210505111525.308018373@infradead.org

diff --git a/Documentation/accounting/delay-accounting.rst b/Documentation/accounting/delay-accounting.rst
index 7cc7f58..f20b282 100644 (file)
--- a/Documentation/accounting/delay-accounting.rst
+++ b/Documentation/accounting/delay-accounting.rst
@@ -69,13 +69,13 @@ Compile the kernel with::
        CONFIG_TASK_DELAY_ACCT=y
        CONFIG_TASKSTATS=y
 
-Delay accounting is enabled by default at boot up.
-To disable, add::
+Delay accounting is disabled by default at boot up.
+To enable, add::
 
-   nodelayacct
+   delayacct
 
 to the kernel boot options. The rest of the instructions
-below assume this has not been done.
+below assume this has been done.
 
 After the system has booted up, use a utility
 similar to  getdelays.c to access the delays

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbd..ef5048c 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3244,7 +3244,7 @@
 
        noclflush       [BUGS=X86] Don't use the CLFLUSH instruction
 
-       nodelayacct     [KNL] Disable per-task delay accounting
+       delayacct       [KNL] Enable per-task delay accounting
 
        nodsp           [SH] Disable hardware DSP at boot time.
 

diff --git a/include/linux/delayacct.h b/include/linux/delayacct.h
index 57fefa5..225c8e0 100644 (file)
--- a/include/linux/delayacct.h
+++ b/include/linux/delayacct.h
@@ -61,7 +61,7 @@ struct task_delay_info {
 #include <linux/jump_label.h>
 
 #ifdef CONFIG_TASK_DELAY_ACCT
-DECLARE_STATIC_KEY_TRUE(delayacct_key);
+DECLARE_STATIC_KEY_FALSE(delayacct_key);
 extern int delayacct_on;       /* Delay accounting turned on/off */
 extern struct kmem_cache *delayacct_cache;
 extern void delayacct_init(void);
@@ -69,7 +69,7 @@ extern void __delayacct_tsk_init(struct task_struct *);
 extern void __delayacct_tsk_exit(struct task_struct *);
 extern void __delayacct_blkio_start(void);
 extern void __delayacct_blkio_end(struct task_struct *);
-extern int __delayacct_add_tsk(struct taskstats *, struct task_struct *);
+extern int delayacct_add_tsk(struct taskstats *, struct task_struct *);
 extern __u64 __delayacct_blkio_ticks(struct task_struct *);
 extern void __delayacct_freepages_start(void);
 extern void __delayacct_freepages_end(void);
@@ -116,7 +116,7 @@ static inline void delayacct_tsk_free(struct task_struct *tsk)
 
 static inline void delayacct_blkio_start(void)
 {
-       if (!static_branch_likely(&delayacct_key))
+       if (!static_branch_unlikely(&delayacct_key))
                return;
 
        delayacct_set_flag(current, DELAYACCT_PF_BLKIO);
@@ -126,7 +126,7 @@ static inline void delayacct_blkio_start(void)
 
 static inline void delayacct_blkio_end(struct task_struct *p)
 {
-       if (!static_branch_likely(&delayacct_key))
+       if (!static_branch_unlikely(&delayacct_key))
                return;
 
        if (p->delays)
@@ -134,14 +134,6 @@ static inline void delayacct_blkio_end(struct task_struct *p)
        delayacct_clear_flag(p, DELAYACCT_PF_BLKIO);
 }
 
-static inline int delayacct_add_tsk(struct taskstats *d,
-                                       struct task_struct *tsk)
-{
-       if (!delayacct_on || !tsk->delays)
-               return 0;
-       return __delayacct_add_tsk(d, tsk);
-}
-
 static inline __u64 delayacct_blkio_ticks(struct task_struct *tsk)
 {
        if (tsk->delays)

diff --git a/kernel/delayacct.c b/kernel/delayacct.c
index 63012fd..3f08690 100644 (file)
--- a/kernel/delayacct.c
+++ b/kernel/delayacct.c
@@ -14,23 +14,23 @@
 #include <linux/delayacct.h>
 #include <linux/module.h>
 
-DEFINE_STATIC_KEY_TRUE(delayacct_key);
-int delayacct_on __read_mostly = 1;    /* Delay accounting turned on/off */
+DEFINE_STATIC_KEY_FALSE(delayacct_key);
+int delayacct_on __read_mostly;        /* Delay accounting turned on/off */
 struct kmem_cache *delayacct_cache;
 
-static int __init delayacct_setup_disable(char *str)
+static int __init delayacct_setup_enable(char *str)
 {
-       delayacct_on = 0;
+       delayacct_on = 1;
        return 1;
 }
-__setup("nodelayacct", delayacct_setup_disable);
+__setup("delayacct", delayacct_setup_enable);
 
 void delayacct_init(void)
 {
        delayacct_cache = KMEM_CACHE(task_delay_info, SLAB_PANIC|SLAB_ACCOUNT);
        delayacct_tsk_init(&init_task);
-       if (!delayacct_on)
-               static_branch_disable(&delayacct_key);
+       if (delayacct_on)
+               static_branch_enable(&delayacct_key);
 }
 
 void __delayacct_tsk_init(struct task_struct *tsk)
@@ -83,7 +83,7 @@ void __delayacct_blkio_end(struct task_struct *p)
        delayacct_end(&delays->lock, &delays->blkio_start, total, count);
 }
 
-int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
+int delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
 {
        u64 utime, stime, stimescaled, utimescaled;
        unsigned long long t2, t3;
@@ -118,6 +118,9 @@ int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
        d->cpu_run_virtual_total =
                (tmp < (s64)d->cpu_run_virtual_total) ? 0 : tmp;
 
+       if (!tsk->delays)
+               return 0;
+
        /* zero XXX_total, non-zero XXX_count implies XXX stat overflowed */
 
        raw_spin_lock_irqsave(&tsk->delays->lock, flags);