linux-kernel - Re: [PATCH] perf tools: Fix bug for perf kvm report without guestmount.

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Date:	Mon, 09 Dec 2013 13:41:26 -0500
From:	Dongsheng Yang <yangds.fnst@...fujitsu.com>
To:	David Ahern <dsahern@...il.com>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tools: Fix bug for perf kvm report without guestmount.

On 12/09/2013 01:06 PM, Dongsheng Yang wrote:
> On 12/08/2013 11:32 PM, David Ahern wrote:
>> On 12/9/13, 10:12 AM, Dongsheng Yang wrote:
>>> On 12/08/2013 10:42 PM, David Ahern wrote:
>>>> On 12/9/13, 8:20 AM, Dongsheng Yang wrote:
>>>>> How about introduce an option named --guestpid? Then we can make the
>>>>> usage of perf kvm
>>>>> more clear:
>>>>>      * perf kvm --guestkallsyms --guestmodules --guestpid
>>>>> [top|record|report]
>>>>>          This usage is for only one guest and will not resolve the
>>>>> symbols from other guests.
>>>>
>>>> If there is only 1 guest then there should not be a problem right? You
>>>> give perf a single guest kallsyms as the "default" and it works.
>>>> --guestpid adds no value in that case.
>>>
>>> Yes, if there is only one guest is running, "default" guest is "the"
>>> guest. Then with my patch in this thread applied, it works well.
>>>
>>> But consider this scenario, there are two guests are running, but we
>>> need to record-report one of them.
>>>
>>> --guestmount can achieve this request, but as a shortcut of guestmount,
>>> --guest{kallysms, modules} dose not
>>> support it well, right? So, I think we can discard the default guest,
>>> and use guestpid in record-report.
>>
>> No.
>>
>> Use cases:
>> 1. one guest
>> --guestkallsyms and --guestmodules apply to default guest; user 
>> should supply files that apply to the one guest. Supplying any other 
>> kallsyms is just nonsense. *NO* other arguments are needed.
>>
>> 2. more than 1 VM, *ALL* VMs running the same kernel
>> --guestkallsyms and --guestmodules apply to default guest; user 
>> should supply files that apply to all of guests. No other arguments 
>> are needed.
>>
>> 3. more than 1 VM, VMs running different kernels. 1+ VMs running the 
>> same kernel
>> --guestmount allows user to supply files that apply to all of guests 
>> based on pid. --guestkallsyms/guestmodules is used for any guest not 
>> showing up in guestmount.
>>
>
> When more than 1 VM, the cases you provided is all about record-report 
> the symbols from __all__ guests. How about I want to record-report one 
> of them?
> Example:
>     There are 2 guests are running different kernels, I want to 
> record-report VM1.
>
> Currently, we can use --guestmount to get the symbols of VM1, but we 
> can not remove the symbols of VM2 from report. It means the percentage 
> of each symbol is not  the symbol only in this VM1.
>
> What I want with introducing guestpid is to record-report the symbols 
> only from VM1, and ignore VM2.
>

Besides, as we provide two usages of perf-kvm in manpage, guestmount-way 
and guest{kallsyms,modules}-way, but the guest{kallsyms, modules} is not 
used when
there is only one guest is running, the guestmount is used in all 
situations, it seems not reasonable. I think we can provide a guestpid 
to make the guestkallsyms-way can be used in any situation.

This way, user can understand and choose the usage easily.

1. one or more guests you want to record-report, --guestmount-way. It 
provides the full functionality of perf kvm.

2. only one guest you want to record-report, --guestmount is also 
available, and there is another usage for this most used case as a 
shortcut , --guest{kallsyms, modules, pid}.

Then the relationship between the two kinds of usage is more clear, 
right? And in this way, we can make the result of perf-kvm more 
foreseeable to user.

>> David
>>
>>
>
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