Re: [PATCH] Enhance perf to collect KVM guest os statistics from host side

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On 03/16/2010 09:48 AM, Zhang, Yanmin wrote:

Excellent, support for guest kernel != host kernel is critical (I can't
remember the last time I ran same kernels).

How would we support multiple guests with different kernels?
With the patch, 'perf kvm report --sort pid" could show
summary statistics for all guest os instances. Then, use
parameter --pid of 'perf kvm record' to collect single problematic instance data.

That certainly works, though automatic association of guest data with guest symbols is friendlier.

diff -Nraup linux-2.6_tipmaster0315/arch/x86/kvm/vmx.c linux-2.6_tipmaster0315_perfkvm/arch/x86/kvm/vmx.c
--- linux-2.6_tipmaster0315/arch/x86/kvm/vmx.c	2010-03-16 08:59:11.825295404 +0800
+++ linux-2.6_tipmaster0315_perfkvm/arch/x86/kvm/vmx.c	2010-03-16 09:01:09.976084492 +0800
@@ -26,6 +26,7 @@
   #include<linux/sched.h>
   #include<linux/moduleparam.h>
   #include<linux/ftrace_event.h>
+#include<linux/perf_event.h>
   #include "kvm_cache_regs.h"
   #include "x86.h"

@@ -3632,6 +3633,43 @@ static void update_cr8_intercept(struct
   	vmcs_write32(TPR_THRESHOLD, irr);
   }

+DEFINE_PER_CPU(int, kvm_in_guest) = {0};
+
+static void kvm_set_in_guest(void)
+{
+	percpu_write(kvm_in_guest, 1);
+}
+
+static int kvm_is_in_guest(void)
+{
+	return percpu_read(kvm_in_guest);
+}

There is already PF_VCPU for this.
Right, but there is a scope between kvm_guest_enter and really running
in guest os, where a perf event might overflow. Anyway, the scope is very
narrow, I will change it to use flag PF_VCPU.

There is also a window between setting the flag and calling 'int $2' where an NMI might happen and be accounted incorrectly.

Perhaps separate the 'int $2' into a direct call into perf and another call for the rest of NMI handling. I don't see how it would work on svm though - AFAICT the NMI is held whereas vmx swallows it. I guess NMIs will be disabled until the next IRET so it isn't racy, just tricky.

+static struct perf_guest_info_callbacks kvm_guest_cbs = {
+	.is_in_guest 		= kvm_is_in_guest,
+	.is_user_mode		= kvm_is_user_mode,
+	.get_guest_ip		= kvm_get_guest_ip,
+	.reset_in_guest		= kvm_reset_in_guest,
+};

Should be in common code, not vmx specific.
Right. I discussed with Yangsheng. I will move above data structures and
callbacks to file arch/x86/kvm/x86.c, and add get_ip, a new callback to
kvm_x86_ops.

You will need access to the vcpu pointer (kvm_rip_read() needs it), you can put it in a percpu variable. I guess if it's not null, you know you're in a guest, so no need for PF_VCPU.

--
error compiling committee.c: too many arguments to function

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