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

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Date:	Tue, 16 Mar 2010 07:41:11 +0200
From:	Avi Kivity <avi@...hat.com>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	oerg Roedel <joro@...tes.org>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, ziteng.huang@...el.com
Subject: Re: [PATCH] Enhance perf to collect KVM guest os statistics from
 host side

On 03/16/2010 07:27 AM, Zhang, Yanmin wrote:
> From: Zhang, Yanmin<yanmin_zhang@...ux.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@...-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.

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