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

[Dongsheng Yang]

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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