RE: [MI] Extending -list-thread-groups --available to show cores

Marc Khouzam
2009-11-09T18:48:36Z

> -----Original Message-----
> From: gdb-owner@sourceware.org
> [mailto:gdb-owner@sourceware.org] On Behalf Of Marc Khouzam
> Sent: Monday, November 09, 2009 12:15 PM
> To: 'Vladimir Prus'
> Cc: 'gdb@sources.redhat.com'
> Subject: RE: [MI] Extending -list-thread-groups --available
> to show cores
>
>
> > -----Original Message-----
> > From: Vladimir Prus [mailto:vladimir@codesourcery.com]
> > Sent: Monday, November 09, 2009 11:29 AM
> > To: Marc Khouzam
> > Cc: 'gdb@sources.redhat.com'
> > Subject: Re: [MI] Extending -list-thread-groups --available
> > to show cores
> >
> > On Monday 09 November 2009 Marc Khouzam wrote:
> >
> > > > > > We were recently asked to slightly extend the
> > returned information
> > > > > > to include the core where each thread runs. Such
> > information is
> > > > > > of little use for typical Linux application, since
> threads are
> > > > > > migrated between cores. However, it's useful for
> both custom
> > > > > > Linux applications that specifically pin threads to
> > > > specific cores,
> > > > > > and for embedded systems. Therefore, I plan to add
> a new field
> > > > > > to the thread information that is output by
> > >
> > > Is there currently thread information in the output of
> > "--available"?
> >
> > No.
>
> Sorry, I had not understood from the spec that you would be adding
> thread information to the output to "--availabe"

I just thought that the -list-thread-group --availabe output is already
very large; if we add threads, it will be huge. What about adding an option
to indicate if threads should be listed or not? Like
-list-thread-groups --available [print-details]
where 'print-details' could be different values that would
indicate what kinds of detail level was requested (like 'threads')?

>
> > > > > > -list-thread-groups --available, named 'core' that
> > will give the
> > > > > > number of the core. E.g.
> > > > >
> > > > > I assume you didn't mean to restrict this output to the
> > > > "--available"
> > > > > form of "-list-thread-groups", but meant to say that it
> > would affect
> > > > > all forms of "-list-thread-groups", right?
> > > >
> > > > I actually did mean to restrict to --available ;-) But if 'core'
> > > > will be beneficial for ordinary '-list-thread-group',
> > please assume
> > > > it's there.
> > >
> > > It is just that in the original email, the examples you gave were
> > > not for the "--available" case :-)
> > >
> > > -list-thread-groups
> > >
> > ^done,groups=[{id="17",type="process",pid="yyy",num_children="
> > 2",cores=[1,2]}]
> > > -list-thread-groups 17
> > > ^done,threads=[{id="2",target-id="Thread 0xb7e14b90
> > (LWP 21257)",cores=[1]
> > >
> > frame={level="0",addr="0xffffe410",func="__kernel_vsyscall",ar
> > gs=[]},state="running"},
> >
> > I've accidentally left out --available; it should be there.
>
> Ok.
> But that means you are also proposing to support:
> -list-thread-groups --available [group]
>
> I'm just clarifying 'cause that is not suported today.
> If fact, you are also suggesting
> -list-thread-groups --available [group1] [group2] ...
> right?
> are you also suggesting
> -list-thread-groups [group1] [group2] ...
> or not?
>
> > > > Yes, "types" should be "type". Basically, we have a
> > > > compatibility issue
> > > > here. Now, -list-thread-groups 17 prints only threads in
> > that process.
> > > > And if we make '-list -thread-groups 17 18' print only
> > threads in one
> > > > list, there will be no way to figure what process each thread
> > > > belongs to.
> > > > We can either:
> > > >
> > > > 1- add 'process' parent link to each thread
> > > > 2- show groups, with threads inside them, as the above
> > output shows
> > > >
> > > > The second approach seems easier for frontend, since it won't
> > > > be required
> > > > to group threads itself. But it makes the output for '17'
> > and '17 18'
> > > > cases be different in structure, so a frontend should be
> > prepared to
> > > > both outputs. Does not seem like we can do much better?
> > >
> > > What about #1 and having multiple "threads=", one for
> each process?
> > > Something like:
> > >
> > > -list-thread-groups 17 18
> > > ^done,threads=[{id="2",group="17", target-id="Thread
> > 0xb7e14b90 (LWP 21257)",cores=[1]
> > >
> > frame={level="0",addr="0xffffe410",func="__kernel_vsyscall",ar
> > gs=[]},state="running"}}],
> > > threads=[{id="3",group="18", target-id="Thread
> > 0xb7e14b90 (LWP 21257)",cores=[1]
> > >
> > frame={level="0",addr="0xfffff410",func="__kernel_vsyscall",ar
> > gs=[]},state="running"}}]
> > >
> > > This would make "-list-thread-groups 17" only get new
> > backwards-compatible fields,
> > > while allowing "-list-thread-groups 17 18" to show threads
> > as part of a grouping.
> > > Does this go against the rules of MI?
> >
> > While there's no explicit rule that names of fields are
> > unique, having them
> > non-unique sounds a bit hacky to me. E.g. KDevelop parser
> > would not even
> > be able to access such fields.
>
> But even if a frontend does not support this format now,
> it is still a backwards compatible solution since having
> non-unique fields would only occur in this case when using
> the new multiple-arg form of -list-thread-groups.
>
> Would it be hard to have this concept supported by KDevelop?
> I didn't try it in DSF-GDB, but since we loop over all fields,
> each field, unique or not, should eventually be accessed, so it
> should work quite easily.
>
> One could argue that if a frontend cannot handle non-unique
> fields, it should limit itself to issuing multiple
> -list-thread-groups <group>
> and not use the new
> -list-thread-groups <group> ...
>
> > > > Well, we probably can declare that -list-thread-groups is
> > so new that
> > > > we can break backward compatibility -- what do you think?
> > >
> > > This is tempting. However, even if no other frontend is
> > using this now,
> > > if a frontend wants to support GDB 7.0 and the next GDB,
> they would
> > > need to code for both outputs. Keeping the output
> > backwards compatible
> > > will allow future frontends that don't want to use mutliple
> > parameters
> > > to -list-thread-groups to have one way of parsing the output.
> >
> > Then, maybe we should trick to the output I have originally
> suggested.
> > It looks like having the frontend recognize both 'groups' and
> > 'threads'
> > as top-level element in response is just as good as having duplicate
> > field names. What do you think?
>
> The reason I prefer duplicate field names is that I don't really like
> the idea of having
> -list-thread-groups group1
> have a different output format than
> -list-thread-groups group1 group2
>
> In my opinion, if it is possible, the two should have the same format,
> as long as backwards-compatibility can be preserved.
>
> But maybe that is just me?
>
> Marc
>
>