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

Avi Kivity
2010-03-16T05:41:36Z

On 03/16/2010 07:27 AM, Zhang, Yanmin wrote:
> From: Zhang, Yanmin<yanmin_zhang@linux.intel.com>
>
> Based on the discussion in KVM community, I worked out the patch to support
> perf to collect guest os statistics from host side. This patch is implemented
> with Ingo, Peter and some other guys' kind help. Yang Sheng pointed out a
> critical bug and provided good suggestions with other guys. I really appreciate
> their kind help.
>
> The patch adds new subcommand kvm to perf.
>
> perf kvm top
> perf kvm record
> perf kvm report
> perf kvm diff
>
> The new perf could profile guest os kernel except guest os user space, but it
> could summarize guest os user space utilization per guest os.
>
> Below are some examples.
> 1) perf kvm top
> [root@lkp-ne01 norm]# perf kvm --host --guest --guestkallsyms=/home/ymzhang/guest/kallsyms
> --guestmodules=/home/ymzhang/guest/modules top
>
>

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? Perhaps a
symbol server that perf can connect to (and that would connect to guests
in turn)?

> 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.

> +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.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.