[PATCH/RFC 3/4, second shot]Introduce "account_guest_time"

[Laurent Vivier <Laurent.Vivier@bull.net>]

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This is another way to compute guest time... I remove the "account modifiers"
mechanism and call directly account_guest_time() from account_system_time().
account_system_time() computes user, system and guest times according value
accumulated in vtime (a ktime_t) in task_struct by the virtual machine.
-- 
------------- Laurent.Vivier@bull.net  --------------
          "Software is hard" - Donald Knuth

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Index: kvm/include/linux/sched.h
===================================================================
--- kvm.orig/include/linux/sched.h	2007-08-17 10:18:53.000000000 +0200
+++ kvm/include/linux/sched.h	2007-08-17 12:33:22.000000000 +0200
@@ -1192,6 +1192,9 @@
 #ifdef CONFIG_FAULT_INJECTION
 	int make_it_fail;
 #endif
+#ifdef CONFIG_GUEST_ACCOUNTING
+	ktime_t vtime;
+#endif
 };
 
 /*
Index: kvm/kernel/sched.c
===================================================================
--- kvm.orig/kernel/sched.c	2007-08-17 10:18:53.000000000 +0200
+++ kvm/kernel/sched.c	2007-08-17 12:33:07.000000000 +0200
@@ -3233,6 +3233,37 @@
 		cpustat->user = cputime64_add(cpustat->user, tmp);
 }
 
+#ifdef CONFIG_GUEST_ACCOUNTING
+/*
+ * Account guest time to a process
+ * @p: the process that the cpu time gets accounted to
+ * @cputime: the cpu time spent in kernel space since the last update
+ */
+
+static cputime_t account_guest_time(struct task_struct *p, cputime_t cputime)
+{
+	struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
+	ktime_t kmsec = ktime_set(0, NSEC_PER_MSEC);
+	cputime_t cmsec = msecs_to_cputime(1);
+
+	while ((ktime_to_ns(p->vtime) >= NSEC_PER_MSEC) &&
+		(cputime_to_msecs(cputime) >= 1)) {
+		p->vtime = ktime_sub(p->vtime, kmsec);
+		p->utime = cputime_add(p->utime, cmsec);
+		p->gtime = cputime_add(p->gtime, cmsec);
+
+		cpustat->guest = cputime64_add(cpustat->guest,
+				cputime_to_cputime64(cmsec));
+		cpustat->user = cputime64_add(cpustat->user,
+		cputime_to_cputime64(cmsec));
+
+		cputime = cputime_sub(cputime, cmsec);
+	}
+
+	return cputime;
+}
+#endif
+
 /*
  * Account system cpu time to a process.
  * @p: the process that the cpu time gets accounted to
@@ -3246,6 +3277,10 @@
 	struct rq *rq = this_rq();
 	cputime64_t tmp;
 
+#ifdef CONFIG_GUEST_ACCOUNTING
+	cputime = account_guest_time(p, cputime);
+#endif
+
 	p->stime = cputime_add(p->stime, cputime);
 
 	/* Add system time to cpustat. */