Re: GSOC Proposal

[nick <xerofoify@gmail.com>]

On 2019-04-01 5:56 a.m., Richard Biener wrote:
> On Fri, 29 Mar 2019, nick wrote:
> 
>>
>>
>> On 2019-03-29 10:28 a.m., nick wrote:
>>>
>>>
>>> On 2019-03-29 5:08 a.m., Richard Biener wrote:
>>>> On Thu, 28 Mar 2019, nick wrote:
>>>>
>>>>>
>>>>>
>>>>> On 2019-03-28 4:59 a.m., Richard Biener wrote:
>>>>>> On Wed, Mar 27, 2019 at 6:31 PM nick <xerofoify@gmail.com> wrote:
>>>>>>>
>>>>>>> Greetings All,
>>>>>>>
>>>>>>> I've already done most of the work required for signing up for GSoC
>>>>>>> as of last year i.e. reading getting started, being signed up legally
>>>>>>> for contributions.
>>>>>>>
>>>>>>> My only real concern would be the proposal which I started writing here:
>>>>>>> https://docs.google.com/document/d/1BKVeh62IpigsQYf_fJqkdu_js0EeGdKtXInkWZ-DtU0/edit?usp=sharing
>>>>>>>
>>>>>>> The biography and success section I'm fine with my bigger concern would be the project and roadmap
>>>>>>> section. The roadmap is there and I will go into more detail about it in the projects section as
>>>>>>> need be. Just wanted to known if the roadmap is detailed enough or can I just write out a few
>>>>>>> paragraphs discussing it in the Projects Section.
>>>>>>
>>>>>> I'm not sure I understand either the problem analysis nor the project
>>>>>> goal parts.  What
>>>>>> shared state with respect to garbage collection are you talking about?
>>>>>>
>>>>>> Richard.
>>>>>>
>>>>> I just fixed it. Seems we were discussing RTL itself. I edited it to 
>>>>> reflect those changes. Let me know if it's unclear or you would actually 
>>>>> like me to discuss some changes that may occur in the RTL layer itself.
>>>>>
>>>>>
>>>>> I'm glad to be more exact if that's better but seems your confusion was 
>>>>> just what layer we were touching.
>>>>
>>>> Let me just throw in some knowledge here.  The issue with RTL
>>>> is that we currently can only have a single function in this
>>>> intermediate language state since a function in RTL has some
>>>> state in global variables that would differ if it were another
>>>> function.  We can have multiple functions in GIMPLE intermediate
>>>> language state since all such state is in a function-specific
>>>> data structure (struct function).  The hard thing about moving
>>>> all this "global" state of RTL into the same place is that
>>>> there's global state in the various backends (and there's
>>>> already a struct funtion 'machine' part for such state, so there's
>>>> hope the issue isn't as big as it could be) and that some of
>>>> the global state is big and only changes very rarely.
>>>> That said, I'm not sure if anybody knows the full details here.
>>>>
>>>> So as far as I understand you'd like to tackle this as project
>>>> with the goal to be able to have multiple functions in RTL
>>>> state.
>>>>
>>>> That's laudable but IMHO also quite ambitious for a GSoC
>>>> project.  It's also an area I am not very familiar with so
>>>> I opt out of being a mentor for this project.
>>>>
>>> While I'm aware of three areas where the shared state is an issue
>>> currently:
>>> 1, Compiler's Proper
>>> 2. The expand_functions 
>>> 3. RTL
>>> 4.Garbage Collector
>>>
>>> Or maybe a project to be more
>>> explicit about regions of the code that assume that the garbage-
>>> collector can't run within them?[3] (since the GC is state that would
>>> be shared by the threads).
>>>
>>> This is what we were discussing previously and I wrote my proposal for
>>> that. You however seem confused about what parts of the garbage collector
>>> would be touched. That's fine with me, however seems you want be to
>>> be more exact about which part  is touched.
>>>
>>> My questions would be as it's changed back to the garbage collector project:
>>> https://docs.google.com/document/d/1BKVeh62IpigsQYf_fJqkdu_js0EeGdKtXInkWZ-DtU0/edit
>>>
>>> 1. Your confusion about which part of the garbage collector is touched doesn't
>>> really make sense s it's for the whole garbage collector as related to shared
>>> state?
>>> 2. Injection was my code here in phase 3 for the callers of the new functions or
>>> macros, perhaps this is not needed as the work with the garbage collector is enough?
>>> 3. Am I not understanding this project as I thought I was in the proposal I wrote?
>>>
>>> Seems your more confusing my wording probably so I'm going to suggest one of 
>>> two things here:
>>> a) I'm going to allow you to make comments with what's confusing you and
>>> it needs that's the issue here more than anything else so I sent you 
>>> a link and please comment where you are having issues with this not
>>> be clear for you:
>>> Or maybe a project to be more
>>> explicit about regions of the code that assume that the garbage-
>>> collector can't run within them?[3] (since the GC is state that would
>>> be shared by the threads).
>>> as that's the actual project
>>>
>>> b) Just comment here about the wording that's an issue for you or
>>> where you want more exact wording
>>>
>>> Sorry and hopefully this is helps you understand where I'm going,
>>> Nick
>>>
>>>> Richard.
>>>>
>>>>> Nick
>>>>>>> Any other comments are welcome as well as I write it there,
>>>>>>> Nick
>>>>>
>>
>> Richard,
>>
>> Seems your right touching the complete garbage collector is too much. I'm
>> just looking at the users of the garbage collector and it seems one of the
>> major ones is pre compiled headers.
>>
>> I've narrowed it down to that. My own real final concern is two things:
>> 1. Does it make sense to you in my writing?
>> 2. Should callers inject the information for state sharing as required
>> as that seems better or is it better for the garbage collector to  store
>> the state sharing flags,marcos and functions internally for this.
>>
>> Thanks and seems I was over thinking the last proposal it's too much:),
> 
> Nick,
> 
> as I've previously explained the garbage collector (and 
> precompiled-headers) workings are understood well and its state
> is already annotated everywhere.  What I do not understand is
> what "global state" with respect to parallelization in GCC you
> refer to when you write about the garbage collector and how
> annotating helps parallelization.  The garbage collector itself
> is only an issue for parallelization as far as it is not
> thread-safe at the moment.  Collection already only happens
> at very specific points where it is known to be safe.
> 
> Richard.
> 
Well I'm talking about the shared roots of this garbage collector core state 
data structure or just struct ggc_root_tab.

But also this seems that this to be no longer shared globally if I'm not mistaken 
or this:
static vec<const_ggc_root_tab_t> extra_root_vec;

Not sure after reading the code which is a bigger deal through so I wrote
my proposal not just asking which is a better issue for not being thread
safe. Sorry about that.

As for the second question injection seems to not be the issue or outside
callers but just internal so phase 3 or step 3 would now be:
Find internal callers or users of x where x is one of the above rather
than injecting outside callers. Which answers my second question about
external callers being a issue still.

Let me know which  of the two is a better issue:
1. struct ggc_root_tabs being shared
2.static vec<const_ggc_root_tab_t> extra_root_vec; as a shared heap or
vector of root nodes for each type of allocation

and I will gladly rewrite my proposal sections for that
as needs to be reedited.

Thanks,
Nick