On Tue, 13 Dec 2016 12:13:22 +0100
Martin Schwidefsky <schwidef...@de.ibm.com> wrote:
> On Mon, 12 Dec 2016 16:02:30 +0100
> Frederic Weisbecker <fweis...@gmail.com> wrote:
>
> > On Mon, Dec 12, 2016 at 11:27:54AM +0100, Martin Schwidefsky wrote:
> > > 3) The call to vtime_flush in account_process_tick is done in irq context
> > > from
> > > update_process_times. hardirq_offset==1 is also correct.
> >
> > Let's see this for example:
> >
> > + if ((tsk->flags & PF_VCPU) && (irq_count() - hardirq_offset == 0))
> > + S390_lowcore.guest_timer += timer;
> >
> > If the tick is interrupting guest, we have accounted the guest time on tick
> > IRQ entry.
> > Now we are in the middle of the tick interrupt and since hardirq_offset is
> > 1, we
> > are taking the above path by accounting half of the tick-IRQ time as guest,
> > which is wrong,
> > it's actually IRQ time.
>
> Hmm, you got me there. The system time from irq_enter until
> account_process_tick
> is reached is indeed IRQ time. It is not much but it is incorrect. The best
> fix
> would be to rip out the accounting of the system time from
> account_process_tick
> as irq_enter / irq_exit will do system time accounting anyway. To do that
> do_account_vtime needs to be split, because for the task switch we need to
> account the system time of the previous task.
New patch for the delayed cputime account. I can not just rip out system time
accounting from account_process_tick after all, I need a sync point for the
steal time calculation. It basically is the same patch as before but with a new
helper update_tsk_timer, the removal of hardirq_offset and a simplification
for do_account_vtime: the last accounting delta is either hardirq time for
the tick or system time for the task switch.
Keeping my finger crossed..
--
>From 2d7ca61909c438f947d27110b7b2a2b67a44607a Mon Sep 17 00:00:00 2001
From: Martin Schwidefsky <schwidef...@de.ibm.com>
Date: Sat, 3 Dec 2016 15:56:50 +0100
Subject: [PATCH 1/2] s390/cputime: delayed accounting of system time
The account_system_time() function is called with a cputime that
occurred while running in the kernel. The function detects which
context the CPU is currently running in and accounts the time to
the correct bucket. This forces the arch code to account the
cputime for hardirq and softirq immediately.
Such accounting function can be costly and perform unwelcome divisions
and multiplications, among others.
The arch code can delay the accounting for system time. For s390
the accounting is done once per timer tick and for each task switch.
Signed-off-by: Martin Schwidefsky <schwidef...@de.ibm.com>
Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Cc: Paul Mackerras <pau...@samba.org>
Cc: Michael Ellerman <m...@ellerman.id.au>
Cc: Heiko Carstens <heiko.carst...@de.ibm.com>
Cc: Martin Schwidefsky <schwidef...@de.ibm.com>
Cc: Tony Luck <tony.l...@intel.com>
Cc: Fenghua Yu <fenghua...@intel.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Rik van Riel <r...@redhat.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Stanislaw Gruszka <sgrus...@redhat.com>
Cc: Wanpeng Li <wanpeng...@hotmail.com>
[rebase against latest cputime tree, massaged changelog accordingly]
---
arch/s390/include/asm/lowcore.h | 65 +++++++++---------
arch/s390/include/asm/processor.h | 3 +
arch/s390/kernel/vtime.c | 134 +++++++++++++++++++++++---------------
3 files changed, 120 insertions(+), 82 deletions(-)
diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h
index 9bfad2a..61261e0 100644
--- a/arch/s390/include/asm/lowcore.h
+++ b/arch/s390/include/asm/lowcore.h
@@ -85,53 +85,56 @@ struct lowcore {
__u64 mcck_enter_timer; /* 0x02c0 */
__u64 exit_timer; /* 0x02c8 */
__u64 user_timer; /* 0x02d0 */
- __u64 system_timer; /* 0x02d8 */
- __u64 steal_timer; /* 0x02e0 */
- __u64 last_update_timer; /* 0x02e8 */
- __u64 last_update_clock; /* 0x02f0 */
- __u64 int_clock; /* 0x02f8 */
- __u64 mcck_clock; /* 0x0300 */
- __u64 clock_comparator; /* 0x0308 */
+ __u64 guest_timer; /* 0x02d8 */
+ __u64 system_timer; /* 0x02e0 */
+ __u64 hardirq_timer; /* 0x02e8 */
+ __u64 softirq_timer; /* 0x02f0 */
+ __u64 steal_timer; /* 0x02f8 */
+ __u64 last_update_timer; /* 0x0300 */
+ __u64 last_update_clock; /* 0x0308 */
+ __u64 int_clock; /* 0x0310 */
+ __u64 mcck_clock; /* 0x0318 */
+ __u64 clock_comparator; /* 0x0320 */
/* Current process. */
- __u64 current_task; /* 0x0310 */
- __u8 pad_0x318[0x320-0x318]; /* 0x0318 */
- __u64 kernel_stack; /* 0x0320 */
+ __u64 current_task; /* 0x0328 */
+ __u8 pad_0x318[0x320-0x318]; /* 0x0330 */
+ __u64 kernel_stack; /* 0x0338 */
/* Interrupt, panic and restart stack. */
- __u64 async_stack; /* 0x0328 */
- __u64 panic_stack; /* 0x0330 */
- __u64 restart_stack; /* 0x0338 */
+ __u64 async_stack; /* 0x0340 */
+ __u64 panic_stack; /* 0x0348 */
+ __u64 restart_stack; /* 0x0350 */
/* Restart function and parameter. */
- __u64 restart_fn; /* 0x0340 */
- __u64 restart_data; /* 0x0348 */
- __u64 restart_source; /* 0x0350 */
+ __u64 restart_fn; /* 0x0358 */
+ __u64 restart_data; /* 0x0360 */
+ __u64 restart_source; /* 0x0368 */
/* Address space pointer. */
- __u64 kernel_asce; /* 0x0358 */
- __u64 user_asce; /* 0x0360 */
+ __u64 kernel_asce; /* 0x0370 */
+ __u64 user_asce; /* 0x0378 */
/*
* The lpp and current_pid fields form a
* 64-bit value that is set as program
* parameter with the LPP instruction.
*/
- __u32 lpp; /* 0x0368 */
- __u32 current_pid; /* 0x036c */
+ __u32 lpp; /* 0x0380 */
+ __u32 current_pid; /* 0x0384 */
/* SMP info area */
- __u32 cpu_nr; /* 0x0370 */
- __u32 softirq_pending; /* 0x0374 */
- __u64 percpu_offset; /* 0x0378 */
- __u64 vdso_per_cpu_data; /* 0x0380 */
- __u64 machine_flags; /* 0x0388 */
- __u32 preempt_count; /* 0x0390 */
- __u8 pad_0x0394[0x0398-0x0394]; /* 0x0394 */
- __u64 gmap; /* 0x0398 */
- __u32 spinlock_lockval; /* 0x03a0 */
- __u32 fpu_flags; /* 0x03a4 */
- __u8 pad_0x03a8[0x0400-0x03a8]; /* 0x03a8 */
+ __u32 cpu_nr; /* 0x0388 */
+ __u32 softirq_pending; /* 0x038c */
+ __u64 percpu_offset; /* 0x0390 */
+ __u64 vdso_per_cpu_data; /* 0x0398 */
+ __u64 machine_flags; /* 0x03a0 */
+ __u32 preempt_count; /* 0x03a8 */
+ __u8 pad_0x03ac[0x03b0-0x03ac]; /* 0x03ac */
+ __u64 gmap; /* 0x03b0 */
+ __u32 spinlock_lockval; /* 0x03b8 */
+ __u32 fpu_flags; /* 0x03bc */
+ __u8 pad_0x03c0[0x0400-0x03c0]; /* 0x03c0 */
/* Per cpu primary space access list */
__u32 paste[16]; /* 0x0400 */
diff --git a/arch/s390/include/asm/processor.h
b/arch/s390/include/asm/processor.h
index 9c00351..6f07907 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -111,7 +111,10 @@ struct thread_struct {
unsigned int acrs[NUM_ACRS];
unsigned long ksp; /* kernel stack pointer */
unsigned long user_timer; /* task cputime in user space */
+ unsigned long guest_timer; /* task cputime in kvm guest */
unsigned long system_timer; /* task cputime in kernel space */
+ unsigned long hardirq_timer; /* task cputime in hardirq context */
+ unsigned long softirq_timer; /* task cputime in softirq context */
unsigned long sys_call_table; /* system call table address */
mm_segment_t mm_segment;
unsigned long gmap_addr; /* address of last gmap fault. */
diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index 6b246aa..65dc7b6 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -90,14 +90,33 @@ static void update_mt_scaling(void)
__this_cpu_write(mt_scaling_jiffies, jiffies_64);
}
+static inline u64 update_tsk_timer(unsigned long *tsk_vtime, u64 new)
+{
+ u64 delta;
+
+ delta = new - *tsk_vtime;
+ *tsk_vtime = new;
+ return delta;
+}
+
+
+static inline u64 scale_vtime(u64 vtime)
+{
+ u64 mult = __this_cpu_read(mt_scaling_mult);
+ u64 div = __this_cpu_read(mt_scaling_div);
+
+ if (smp_cpu_mtid)
+ return vtime * mult / div;
+ return vtime;
+}
+
/*
* Update process times based on virtual cpu times stored by entry.S
* to the lowcore fields user_timer, system_timer & steal_clock.
*/
-static int do_account_vtime(struct task_struct *tsk, int hardirq_offset)
+static int do_account_vtime(struct task_struct *tsk)
{
- u64 timer, clock, user, system, steal;
- u64 user_scaled, system_scaled;
+ u64 timer, clock, user, guest, system, hardirq, softirq, steal;
timer = S390_lowcore.last_update_timer;
clock = S390_lowcore.last_update_clock;
@@ -110,36 +129,53 @@ static int do_account_vtime(struct task_struct *tsk, int
hardirq_offset)
#endif
: "=m" (S390_lowcore.last_update_timer),
"=m" (S390_lowcore.last_update_clock));
- S390_lowcore.system_timer += timer - S390_lowcore.last_update_timer;
- S390_lowcore.steal_timer += S390_lowcore.last_update_clock - clock;
+ clock = S390_lowcore.last_update_clock - clock;
+ timer -= S390_lowcore.last_update_timer;
+
+ if (hardirq_count())
+ S390_lowcore.hardirq_timer += timer;
+ else
+ S390_lowcore.system_timer += timer;
/* Update MT utilization calculation */
if (smp_cpu_mtid &&
time_after64(jiffies_64, this_cpu_read(mt_scaling_jiffies)))
update_mt_scaling();
- user = S390_lowcore.user_timer - tsk->thread.user_timer;
- S390_lowcore.steal_timer -= user;
- tsk->thread.user_timer = S390_lowcore.user_timer;
-
- system = S390_lowcore.system_timer - tsk->thread.system_timer;
- S390_lowcore.steal_timer -= system;
- tsk->thread.system_timer = S390_lowcore.system_timer;
-
- user_scaled = user;
- system_scaled = system;
- /* Do MT utilization scaling */
- if (smp_cpu_mtid) {
- u64 mult = __this_cpu_read(mt_scaling_mult);
- u64 div = __this_cpu_read(mt_scaling_div);
+ /* Calculate cputime delta */
+ user = update_tsk_timer(&tsk->thread.user_timer,
+ READ_ONCE(S390_lowcore.user_timer));
+ guest = update_tsk_timer(&tsk->thread.guest_timer,
+ READ_ONCE(S390_lowcore.guest_timer));
+ system = update_tsk_timer(&tsk->thread.system_timer,
+ READ_ONCE(S390_lowcore.system_timer));
+ hardirq = update_tsk_timer(&tsk->thread.hardirq_timer,
+ READ_ONCE(S390_lowcore.hardirq_timer));
+ softirq = update_tsk_timer(&tsk->thread.softirq_timer,
+ READ_ONCE(S390_lowcore.softirq_timer));
+ S390_lowcore.steal_timer +=
+ clock - user - guest - system - hardirq - softirq;
+
+ /* Push account value */
+ if (user) {
+ account_user_time(tsk, user);
+ tsk->utimescaled += scale_vtime(user);
+ }
- user_scaled = (user_scaled * mult) / div;
- system_scaled = (system_scaled * mult) / div;
+ if (guest) {
+ account_guest_time(tsk, guest);
+ tsk->utimescaled += scale_vtime(guest);
}
- account_user_time(tsk, user);
- tsk->utimescaled += user_scaled;
- account_system_time(tsk, hardirq_offset, system);
- tsk->stimescaled += system_scaled;
+
+ if (system)
+ account_system_index_scaled(tsk, system, scale_vtime(system),
+ CPUTIME_SYSTEM);
+ if (hardirq)
+ account_system_index_scaled(tsk, hardirq, scale_vtime(hardirq),
+ CPUTIME_IRQ);
+ if (softirq)
+ account_system_index_scaled(tsk, softirq, scale_vtime(softirq),
+ CPUTIME_SOFTIRQ);
steal = S390_lowcore.steal_timer;
if ((s64) steal > 0) {
@@ -147,16 +183,22 @@ static int do_account_vtime(struct task_struct *tsk, int
hardirq_offset)
account_steal_time(steal);
}
- return virt_timer_forward(user + system);
+ return virt_timer_forward(user + guest + system + hardirq + softirq);
}
void vtime_task_switch(struct task_struct *prev)
{
- do_account_vtime(prev, 0);
+ do_account_vtime(prev);
prev->thread.user_timer = S390_lowcore.user_timer;
+ prev->thread.guest_timer = S390_lowcore.guest_timer;
prev->thread.system_timer = S390_lowcore.system_timer;
+ prev->thread.hardirq_timer = S390_lowcore.hardirq_timer;
+ prev->thread.softirq_timer = S390_lowcore.softirq_timer;
S390_lowcore.user_timer = current->thread.user_timer;
+ S390_lowcore.guest_timer = current->thread.guest_timer;
S390_lowcore.system_timer = current->thread.system_timer;
+ S390_lowcore.hardirq_timer = current->thread.hardirq_timer;
+ S390_lowcore.softirq_timer = current->thread.softirq_timer;
}
/*
@@ -166,7 +208,7 @@ void vtime_task_switch(struct task_struct *prev)
*/
void vtime_account_user(struct task_struct *tsk)
{
- if (do_account_vtime(tsk, HARDIRQ_OFFSET))
+ if (do_account_vtime(tsk))
virt_timer_expire();
}
@@ -176,32 +218,22 @@ void vtime_account_user(struct task_struct *tsk)
*/
void vtime_account_irq_enter(struct task_struct *tsk)
{
- u64 timer, system, system_scaled;
+ u64 timer;
timer = S390_lowcore.last_update_timer;
S390_lowcore.last_update_timer = get_vtimer();
- S390_lowcore.system_timer += timer - S390_lowcore.last_update_timer;
-
- /* Update MT utilization calculation */
- if (smp_cpu_mtid &&
- time_after64(jiffies_64, this_cpu_read(mt_scaling_jiffies)))
- update_mt_scaling();
-
- system = S390_lowcore.system_timer - tsk->thread.system_timer;
- S390_lowcore.steal_timer -= system;
- tsk->thread.system_timer = S390_lowcore.system_timer;
- system_scaled = system;
- /* Do MT utilization scaling */
- if (smp_cpu_mtid) {
- u64 mult = __this_cpu_read(mt_scaling_mult);
- u64 div = __this_cpu_read(mt_scaling_div);
-
- system_scaled = (system_scaled * mult) / div;
- }
- account_system_time(tsk, 0, system);
- tsk->stimescaled += system_scaled;
-
- virt_timer_forward(system);
+ timer -= S390_lowcore.last_update_timer;
+
+ if ((tsk->flags & PF_VCPU) && (irq_count() == 0))
+ S390_lowcore.guest_timer += timer;
+ else if (hardirq_count())
+ S390_lowcore.hardirq_timer += timer;
+ else if (in_serving_softirq())
+ S390_lowcore.softirq_timer += timer;
+ else
+ S390_lowcore.system_timer += timer;
+
+ virt_timer_forward(timer);
}
EXPORT_SYMBOL_GPL(vtime_account_irq_enter);
--
2.8.4
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
