linux-kernel - Re: [PATCH 3/3] KVM: perf: kvm events analysis tool

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Date:	Thu, 16 Feb 2012 13:33:47 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	David Ahern <dsahern@...il.com>
CC:	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 3/3] KVM: perf: kvm events analysis tool

On 02/16/2012 01:05 PM, David Ahern wrote:

> On 2/15/12 9:59 PM, Xiao Guangrong wrote:
>>
>>
>> Okay, i will post the next version after collecting your new comments!
>>
>> Thanks for your time, David! :)
>>
> 
> I had more comments, but got sidetracked and forgot to come back to this. I still haven't looked at the code yet, but some comments from testing:
> 
> 1. The error message:
>   Warning: Error: expected type 5 but read 4
>   Warning: Error: expected type 5 but read 0
>   Warning: unknown op '}'
> 
> is fixed by this patch which has not yet made its way into perf:
> https://lkml.org/lkml/2011/9/4/41
> 
> The most recent request:
> https://lkml.org/lkml/2012/2/8/479
> 
> Arnaldo: the patch still applies cleanly (but with an offset of -2 lines).
> 


Great, it is a good fix.

But, it does not hurt the development of kvm-events.

> 
> 2. negatve testing:
> 
> perf kvm-events record -e kvm:* -p 2603 -- sleep 10
> 
>   Warning: Error: expected type 4 but read 7
>   Warning: Error: expected type 5 but read 0
>   Warning: failed to read event print fmt for kvm_apic
>   Warning: Error: expected type 4 but read 7
>   Warning: Error: expected type 5 but read 0
>   Warning: failed to read event print fmt for kvm_inj_exception
>   Fatal: bad op token {
> 
> If other kvm events are specified in the record line they appear to be silently ignored in the report in which case why allow the -e option to record?
> 


Yes, kvm-events doese not analyse these events specified by -e option since
these events are not needed by vmexit/ioport/mmio analysis.

And after kvm-evnets record, you can see these events by perf script

> 
> 3. What is happening for multiple VMs?
> 
> a. perf kvm-events report
> data is collected for all VMs. What is displayed in the report? An
> average for all VMs?
> 


Yes

> b. perf kvm-events report --vcpu 1
> Does this given an average of all vcpu 1's?
> 


Yes

> Perhaps a -p option for the report to pull out events related to a single VM. Really this could be a generic option (to perf-report and perf-script as well) to only show/analyze events for the specified pid. ie., data is recorded for all VMs (or system wide for the regular perf-record) and you want to only consider events for a specific pid. e.g., in process_sample_event() skip event if event->ip.pid != report_pid (works for perf code because PERF_SAMPLE_TID attribute is always set).

Analysis for per VMs is good idea, but please allow me put it into my TODO list. :)

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