Re: [Xen-devel] [PATCH 1/2] cpu steal time accounting

[Rik van Riel <riel@xxxxxxxxxx>]

On Wed, 22 Feb 2006, Keir Fraser wrote:

> I think the calculation of delta stolen time would be clearer as:
>  ((system_time - prev_system_time) - (vcpu_time - prev_vcpu_time)) /
> NS_PER_TICK

The "(system_time - prev_system_time)" above is equivalent
to the delta_cpu variable.

I agree on saving the prev_vcpu_time though, it makes the code
quite a bit nicer.  I hope you like this patch ;)


Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>


--- linux-2.6.15.i686/arch/i386/kernel/time-xen.c.steal 2006-02-17 
16:44:40.000000000 -0500
+++ linux-2.6.15.i686/arch/i386/kernel/time-xen.c       2006-02-24 
13:53:08.000000000 -0500
@@ -48,6 +48,7 @@
 #include <linux/mca.h>
 #include <linux/sysctl.h>
 #include <linux/percpu.h>
+#include <linux/kernel_stat.h>
 
 #include <asm/io.h>
 #include <asm/smp.h>
@@ -77,6 +78,7 @@
 #include <asm/arch_hooks.h>
 
 #include <xen/evtchn.h>
+#include <xen/interface/vcpu.h>
 
 #if defined (__i386__)
 #include <asm/i8259.h>
@@ -125,6 +127,9 @@ static u32 shadow_tv_version;
 static u64 processed_system_time;   /* System time (ns) at last processing. */
 static DEFINE_PER_CPU(u64, processed_system_time);
 
+/* Keep track of how much time our vcpu used, for steal time calculation. */
+static DEFINE_PER_CPU(u64, prev_vcpu_time);
+
 /* Must be signed, as it's compared with s64 quantities which can be -ve. */
 #define NS_PER_TICK (1000000000LL/HZ)
 
@@ -624,7 +629,32 @@ irqreturn_t timer_interrupt(int irq, voi
          * Local CPU jiffy work. No need to hold xtime_lock, and I'm not sure
          * if there is risk of deadlock if we do (since update_process_times
          * may do scheduler rebalancing work and thus acquire runqueue locks).
+        *
+        * If we have not run for a while, chances are this vcpu got scheduled
+        * away.  Try to estimate how much time was stolen.
          */
+       if (delta_cpu > (s64)(2 * NS_PER_TICK)) {
+               dom0_getvcpuinfo_t vcpu = { 0, };
+               s64 steal;
+               u64 dvcpu;
+
+               if (HYPERVISOR_vcpu_op(VCPUOP_cpu_info, cpu, &vcpu) == 0) {
+                       dvcpu = vcpu.cpu_time - per_cpu(prev_vcpu_time, cpu);
+                       per_cpu(prev_vcpu_time, cpu) = vcpu.cpu_time;
+                       steal = delta_cpu - (s64)dvcpu;
+
+                       if (steal > 0) {
+                               /* do_div modifies the variable in place. */
+                               do_div(steal, NS_PER_TICK);
+
+                               delta_cpu -= steal * NS_PER_TICK;
+                               per_cpu(processed_system_time, cpu) +=
+                                                       steal * NS_PER_TICK;
+                               account_steal_time(current, (cputime_t)steal);
+                       }
+               }
+       }
+
        while (delta_cpu >= NS_PER_TICK) {
                delta_cpu -= NS_PER_TICK;
                per_cpu(processed_system_time, cpu) += NS_PER_TICK;
--- linux-2.6.15.i686/include/xen/interface/vcpu.h.steal        2006-02-17 
16:14:17.000000000 -0500
+++ linux-2.6.15.i686/include/xen/interface/vcpu.h      2006-02-17 
16:14:52.000000000 -0500
@@ -51,6 +51,14 @@
 /* Returns 1 if the given VCPU is up. */
 #define VCPUOP_is_up                3
 
+/*
+ * Get information on how much CPU time this VCPU has used, etc...
+ *
+ * @extra_arg == pointer to an empty dom0_getvcpuinfo_t, the "OUT" variables
+ *               of which filled in with scheduler info.
+ */
+#define VCPUOP_cpu_info             4
+
 #endif /* __XEN_PUBLIC_VCPU_H__ */
 
 /*

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