[PATCH/RFC 9/9] Fix system<->user misaccount of interpreted execution

Carsten Otte
2007-05-11T17:36:10Z

From: Christian Borntraeger <cborntra-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>

This patches fixes the accouting of guest cpu time. As sie is executed via a
system call, all guest operations were accounted as system time. To fix this
we define a per thread "sie context". Before issuing the sie instruction we
enter this context and leave the context afterwards. sie_enter and sie_exit
call account_system_vtime, which now checks for being in sie_context. We
define the sie_context to be accounted as user time.

Possible future enhancement: We could add an additional field: "interpretion
time" to cpu stat and process time. Thus we could differentiate between user
time in the host and host user time spent for guests. The main challenge is
the necessary user space change. Therefore, we could export the interpretion
time with a new interface. To be defined.

Signed-off-By: Christian Borntraeger <cborntra-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>
Signed-off-By: Carsten Otte <cotte-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>

---
arch/s390/Kconfig | 1 +
arch/s390/host/s390host.c | 15 +++++++++++++++
arch/s390/kernel/process.c | 1 +
arch/s390/kernel/vtime.c | 11 ++++++++++-
include/asm-s390/thread_info.h | 2 ++
5 files changed, 29 insertions(+), 1 deletion(-)

Index: linux-2.6.21/arch/s390/kernel/vtime.c
===================================================================
--- linux-2.6.21.orig/arch/s390/kernel/vtime.c
+++ linux-2.6.21/arch/s390/kernel/vtime.c
@@ -97,6 +97,11 @@ void account_vtime(struct task_struct *t
account_system_time(tsk, 0, cputime);
}

+static inline int task_is_in_sie(struct thread_info *thread)
+{
+ return thread->in_sie;
+}
+
/*
* Update process times based on virtual cpu times stored by entry.S
* to the lowcore fields user_timer, system_timer & steal_clock.
@@ -114,7 +119,11 @@ void account_system_vtime(struct task_st
cputime = S390_lowcore.system_timer >> 12;
S390_lowcore.system_timer -= cputime << 12;
S390_lowcore.steal_clock -= cputime << 12;
- account_system_time(tsk, 0, cputime);
+
+ if (task_is_in_sie(tsk->thread_info) && !hardirq_count() && !softirq_count())
+ account_user_time(tsk, cputime);
+ else
+ account_system_time(tsk, 0, cputime);
}

static inline void set_vtimer(__u64 expires)
Index: linux-2.6.21/arch/s390/host/s390host.c
===================================================================
--- linux-2.6.21.orig/arch/s390/host/s390host.c
+++ linux-2.6.21/arch/s390/host/s390host.c
@@ -27,6 +27,19 @@ static int s390host_do_action(unsigned l

static DEFINE_MUTEX(s390host_init_mutex);

+static void enter_sie(void)
+{
+ account_system_vtime(current);
+ current_thread_info()->in_sie = 1;
+}
+
+static void exit_sie(void)
+{
+ account_system_vtime(current);
+ current_thread_info()->in_sie = 0;
+}
+
+
static void s390host_get_data(struct s390host_data *data)
{
atomic_inc(&data->count);
@@ -297,7 +310,9 @@ again:
schedule();

sie_kernel->sie_block.icptcode = 0;
+ enter_sie();
ret = sie64a(sie_kernel);
+ exit_sie();
if (ret)
goto out;

Index: linux-2.6.21/include/asm-s390/thread_info.h
===================================================================
--- linux-2.6.21.orig/include/asm-s390/thread_info.h
+++ linux-2.6.21/include/asm-s390/thread_info.h
@@ -55,6 +55,7 @@ struct thread_info {
struct restart_block restart_block;
struct s390host_data *s390host_data; /* s390host data */
int sie_cpu; /* sie cpu number */
+ int in_sie; /* 1 => cpu is in sie*/
};

/*
@@ -72,6 +73,7 @@ struct thread_info {
}, \
.s390host_data = NULL, \
.sie_cpu = 0, \
+ .in_sie = 0, \
}

#define init_thread_info (init_thread_union.thread_info)
Index: linux-2.6.21/arch/s390/kernel/process.c
===================================================================
--- linux-2.6.21.orig/arch/s390/kernel/process.c
+++ linux-2.6.21/arch/s390/kernel/process.c
@@ -278,6 +278,7 @@ int copy_thread(int nr, unsigned long cl
memset(&p->thread.per_info,0,sizeof(p->thread.per_info));
p->thread_info->s390host_data = NULL;
p->thread_info->sie_cpu = -1;
+ p->thread_info->in_sie = 0;

return 0;
}
Index: linux-2.6.21/arch/s390/Kconfig
===================================================================
--- linux-2.6.21.orig/arch/s390/Kconfig
+++ linux-2.6.21/arch/s390/Kconfig
@@ -519,6 +519,7 @@ config S390_HOST
bool "s390 host support (EXPERIMENTAL)"
depends on 64BIT && EXPERIMENTAL
select S390_SWITCH_AMODE
+ select VIRT_CPU_ACCOUNTING
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