note: you don't have to implement on-all-processors, i can do that in gerbil stdlib; but pinning needs to be exposed in some way (## procedures are fine).
-- vyzo
On Fri, Feb 2, 2018 at 3:42 PM, Dimitris Vyzovitis vyzo@hackzen.org wrote:
pinning, if exposed, should be sufficient to implement it purely in userland.
it would be immediately useful for my heap dumper -- i could use it to get a vector of stills from all processors with the count-still-objects/get-still-objects procedures before starting the walk and use that to ensure that all stills (at the beginning of the walk) are accounted for.
it would also be useful for implementing a parallel dispatch primitive that utilizes all cores maximally. say you have a parallel algorithm that you want to decompose into per core tasks, that could be accomplished with on-all-processors (or a similar primitive based on pinning). and it doesn't have to be a compute algorithm, i/o could benefit too.
-- vyzo
On Fri, Feb 2, 2018 at 3:32 PM, Marc Feeley feeley@iro.umontreal.ca wrote:
The SMP scheduler support “pinning” threads to processors, so perhaps this is implementable. However… why do you need this? I don’t like exposing the processor concept or pinning, which are low-level concepts.
Marc
On Feb 2, 2018, at 8:07 AM, Dimitris Vyzovitis vyzo@hackzen.org
wrote:
perhaps the "don't switch" semantics are too much. a simpler general purpose primitive would be an `on-all-processors`
that spawns
a thread on each processor to execute the thunk and completes when all
thunks
have completed.
that's likely implementable without any deep support from the runtime.
-- vyzo
On Fri, Feb 2, 2018 at 3:00 PM, Dimitris Vyzovitis vyzo@hackzen.org
wrote:
well, perhaps we can think about the right primitive for Scheme level
operations.
the semantics could be something like "execute this thunk on all
processors, and
don't do any switches until it has finished executing".
-- vyzo
On Fri, Feb 2, 2018 at 2:57 PM, Marc Feeley feeley@iro.umontreal.ca
wrote:
on_all_processors was designed for the lowest-level of the runtime
system, I don’t think it is possible for the operation to be in Scheme (I’ll have to thinks about what the constraints are on the operation).
Marc
On Feb 2, 2018, at 7:49 AM, Dimitris Vyzovitis vyzo@hackzen.org
wrote:
it would be nice to have a primitive to do this for Scheme procedures! Something like (on-all-processors thunk) would be awesome.
-- vyzo
On Fri, Feb 2, 2018 at 2:41 PM, Marc Feeley feeley@iro.umontreal.ca
wrote:
Yes each processor has its own still_objs list and to account for all
still objects you must iterate over the processors. In order to avoid modification of the still_objs lists while doing this the best approach is to use the barrier operation mechanism. That way all processors (but one) will be idle while iterating (or you could have all processors cooperate). This is done with the “on_all_processors” function. For an example, check out ___garbage_collect or ___fdset_resize in lib/setup.c .
Marc
On Feb 2, 2018, at 6:23 AM, Dimitris Vyzovitis vyzo@hackzen.org
wrote:
Relevant code for accounting still objects: https://gist.github.com/vyzo/ab4219382c0870779991d4c701921d2c
The limitation is that the still_objs_ is per processor, and not
vm-wide.
Does that mean we would have to crawl all processors in SMP?
-- vyzo
On Thu, Feb 1, 2018 at 3:16 PM, Marc Feeley <
feeley@iro.umontreal.ca> wrote:
On Feb 1, 2018, at 8:06 AM, Dimitris Vyzovitis vyzo@hackzen.org
wrote:
thanks Guillaume!
this is a great start for me -- i am helping fare debug a memory
leak, and it's really hard to identify
without dumping the heap to see what kind of object is leaking.
For your information I discovered a few memory leaks with the
networking functions. They were due to “sockaddr” structures being converted to “still” Scheme objects with a reference count = 1, but the reference count was never decremented (with ___release_scmobj). This has been fixed in the recent UDP commit.
I believe that this kind of situation might exist in other places
in the runtime system. So it might be useful to debug this to have a function that returns a list of all the “still” Scheme objects that have a reference count != 0. This should be easy to write… the GC maintains a list of the still objects in the C variable “still_objs”.
So the idea would be to check at the end of a program if there are
any still objects with non-zero ref counts.
Marc