This is a note to let you know that I've just added the patch titled
sched/cputime: Accumulate vtime on top of nsec clocksource
to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-cputime-accumulate-vtime-on-top-of-nsec-clocksource.patch
and it can be found in the queue-4.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2a42eb9594a1480b4ead9e036e06ee1290e5fa6d Mon Sep 17 00:00:00 2001
From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
Date: Thu, 29 Jun 2017 19:15:11 +0200
Subject: sched/cputime: Accumulate vtime on top of nsec clocksource
From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
commit 2a42eb9594a1480b4ead9e036e06ee1290e5fa6d upstream.
Currently the cputime source used by vtime is jiffies. When we cross
a context boundary and jiffies have changed since the last snapshot, the
pending cputime is accounted to the switching out context.
This system works ok if the ticks are not aligned across CPUs. If they
instead are aligned (ie: all fire at the same time) and the CPUs run in
userspace, the jiffies change is only observed on tick exit and therefore
the user cputime is accounted as system cputime. This is because the
CPU that maintains timekeeping fires its tick at the same time as the
others. It updates jiffies in the middle of the tick and the other CPUs
see that update on IRQ exit:
CPU 0 (timekeeper) CPU 1
------------------- -------------
jiffies = N
... run in userspace for a jiffy
tick entry tick entry (sees jiffies = N)
set jiffies = N + 1
tick exit tick exit (sees jiffies = N + 1)
account 1 jiffy as stime
Fix this with using a nanosec clock source instead of jiffies. The
cputime is then accumulated and flushed everytime the pending delta
reaches a jiffy in order to mitigate the accounting overhead.
[ fweisbec: changelog, rebase on struct vtime, field renames, add delta
on cputime readers, keep idle vtime as-is (low overhead accounting),
harmonize clock sources. ]
Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reported-by: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
Tested-by: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Wanpeng Li <kernellwp@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1498756511-11714-6-git-send-email-fweisbec@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 3 ++
kernel/sched/cputime.c | 64 ++++++++++++++++++++++++++++++++-----------------
2 files changed, 45 insertions(+), 22 deletions(-)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -236,6 +236,9 @@ struct vtime {
seqcount_t seqcount;
unsigned long long starttime;
enum vtime_state state;
+ u64 utime;
+ u64 stime;
+ u64 gtime;
};
struct sched_info {
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -681,18 +681,19 @@ void thread_group_cputime_adjusted(struc
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
static u64 vtime_delta(struct vtime *vtime)
{
- unsigned long now = READ_ONCE(jiffies);
+ unsigned long long clock;
- if (time_before(now, (unsigned long)vtime->starttime))
+ clock = sched_clock_cpu(smp_processor_id());
+ if (clock < vtime->starttime)
return 0;
- return jiffies_to_nsecs(now - vtime->starttime);
+ return clock - vtime->starttime;
}
static u64 get_vtime_delta(struct vtime *vtime)
{
- unsigned long now = READ_ONCE(jiffies);
- u64 delta, other;
+ u64 delta = vtime_delta(vtime);
+ u64 other;
/*
* Unlike tick based timing, vtime based timing never has lost
@@ -701,17 +702,31 @@ static u64 get_vtime_delta(struct vtime
* elapsed time. Limit account_other_time to prevent rounding
* errors from causing elapsed vtime to go negative.
*/
- delta = jiffies_to_nsecs(now - vtime->starttime);
other = account_other_time(delta);
WARN_ON_ONCE(vtime->state == VTIME_INACTIVE);
- vtime->starttime = now;
+ vtime->starttime += delta;
return delta - other;
}
-static void __vtime_account_system(struct task_struct *tsk)
+static void __vtime_account_system(struct task_struct *tsk,
+ struct vtime *vtime)
{
- account_system_time(tsk, irq_count(), get_vtime_delta(&tsk->vtime));
+ vtime->stime += get_vtime_delta(vtime);
+ if (vtime->stime >= TICK_NSEC) {
+ account_system_time(tsk, irq_count(), vtime->stime);
+ vtime->stime = 0;
+ }
+}
+
+static void vtime_account_guest(struct task_struct *tsk,
+ struct vtime *vtime)
+{
+ vtime->gtime += get_vtime_delta(vtime);
+ if (vtime->gtime >= TICK_NSEC) {
+ account_guest_time(tsk, vtime->gtime);
+ vtime->gtime = 0;
+ }
}
void vtime_account_system(struct task_struct *tsk)
@@ -722,7 +737,11 @@ void vtime_account_system(struct task_st
return;
write_seqcount_begin(&vtime->seqcount);
- __vtime_account_system(tsk);
+ /* We might have scheduled out from guest path */
+ if (current->flags & PF_VCPU)
+ vtime_account_guest(tsk, vtime);
+ else
+ __vtime_account_system(tsk, vtime);
write_seqcount_end(&vtime->seqcount);
}
@@ -731,8 +750,7 @@ void vtime_user_enter(struct task_struct
struct vtime *vtime = &tsk->vtime;
write_seqcount_begin(&vtime->seqcount);
- if (vtime_delta(vtime))
- __vtime_account_system(tsk);
+ __vtime_account_system(tsk, vtime);
vtime->state = VTIME_USER;
write_seqcount_end(&vtime->seqcount);
}
@@ -742,8 +760,11 @@ void vtime_user_exit(struct task_struct
struct vtime *vtime = &tsk->vtime;
write_seqcount_begin(&vtime->seqcount);
- if (vtime_delta(vtime))
- account_user_time(tsk, get_vtime_delta(vtime));
+ vtime->utime += get_vtime_delta(vtime);
+ if (vtime->utime >= TICK_NSEC) {
+ account_user_time(tsk, vtime->utime);
+ vtime->utime = 0;
+ }
vtime->state = VTIME_SYS;
write_seqcount_end(&vtime->seqcount);
}
@@ -759,8 +780,7 @@ void vtime_guest_enter(struct task_struc
* that can thus safely catch up with a tickless delta.
*/
write_seqcount_begin(&vtime->seqcount);
- if (vtime_delta(vtime))
- __vtime_account_system(tsk);
+ __vtime_account_system(tsk, vtime);
current->flags |= PF_VCPU;
write_seqcount_end(&vtime->seqcount);
}
@@ -771,7 +791,7 @@ void vtime_guest_exit(struct task_struct
struct vtime *vtime = &tsk->vtime;
write_seqcount_begin(&vtime->seqcount);
- __vtime_account_system(tsk);
+ vtime_account_guest(tsk, vtime);
current->flags &= ~PF_VCPU;
write_seqcount_end(&vtime->seqcount);
}
@@ -794,7 +814,7 @@ void arch_vtime_task_switch(struct task_
write_seqcount_begin(&vtime->seqcount);
vtime->state = VTIME_SYS;
- vtime->starttime = jiffies;
+ vtime->starttime = sched_clock_cpu(smp_processor_id());
write_seqcount_end(&vtime->seqcount);
}
@@ -806,7 +826,7 @@ void vtime_init_idle(struct task_struct
local_irq_save(flags);
write_seqcount_begin(&vtime->seqcount);
vtime->state = VTIME_SYS;
- vtime->starttime = jiffies;
+ vtime->starttime = sched_clock_cpu(cpu);
write_seqcount_end(&vtime->seqcount);
local_irq_restore(flags);
}
@@ -825,7 +845,7 @@ u64 task_gtime(struct task_struct *t)
gtime = t->gtime;
if (vtime->state == VTIME_SYS && t->flags & PF_VCPU)
- gtime += vtime_delta(vtime);
+ gtime += vtime->gtime + vtime_delta(vtime);
} while (read_seqcount_retry(&vtime->seqcount, seq));
@@ -866,9 +886,9 @@ void task_cputime(struct task_struct *t,
* the right place.
*/
if (vtime->state == VTIME_USER || t->flags & PF_VCPU)
- *utime += delta;
+ *utime += vtime->utime + delta;
else if (vtime->state == VTIME_SYS)
- *stime += delta;
+ *stime += vtime->stime + delta;
} while (read_seqcount_retry(&vtime->seqcount, seq));
}
#endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */
Patches currently in stable-queue which might be from wanpeng.li@xxxxxxxxxxx are
queue-4.12/sched-cputime-accumulate-vtime-on-top-of-nsec-clocksource.patch