Proposal: provide cas and barriers symbols even without -threaded

[Carter Schonwald]

nvm, githubs backup, i'll have a look! :)


On Sat, Aug 3, 2013 at 9:05 PM, Carter Schonwald <carter.schonwald at gmail.com
> wrote:

> awesome! (this will also make my work easier)
>
> ryan: github is down, could you put the branch on bitbucket or some such
> so I can have a lookseee/clone locally?
>
> thanks!
> -Carter
>
>
> On Sat, Aug 3, 2013 at 4:01 AM, Ryan Newton <rrnewton at gmail.com> wrote:
>
>> Just to keep you all up to date...  I'm adding the primops in question
>> and validating the individual commits before putting them here:
>>
>>     https://github.com/rrnewton/ghc/commits/atomicPrimOps
>>
>> The basic idea for using these extensions is:
>>
>>    - the atomic-primops library will work in 7.6 or 7.7+.  It will use
>>    ifdefs to decide whether to use its own primops or GHC-builtin
>>    - future versions will simply get faster, as Carter replaces
>>    out-of-line primops that *also* use C calls, with inline primops / LLVM
>>    equivalents
>>
>> Shall I stick a patch on a ticket, or will someone volunteer to pull?
>>  What's the protocol for requesting commit access anyway?  (By the way, can
>> someone share the reason that pull-requests to the github ghc mirror are
>> such a no-no?  They seem no worse than a patch in an email which the big warning
>> sign <https://github.com/ghc/ghc> recommends.)
>>
>> Best,
>>   -Ryan
>>
>> P.S. FYI, I'm periodically getting these:
>>
>>     0 caused framework failures
>>     0 unexpected passes
>>     1 unexpected failures
>>
>>      Unexpected failures:
>>  perf/compiler  T1969 [stat not good enough] (normal)
>>
>> Can that just be because of running on a loaded machine?  How narrow are
>> these windows?
>>
>>
>> On Thu, Aug 1, 2013 at 12:32 PM, Ryan Newton <rrnewton at gmail.com> wrote:
>>
>>> On Sun, Jul 21, 2013 at 3:32 AM, Carter Schonwald <
>>> carter.schonwald at gmail.com> wrote:
>>>
>>>> ok, could you add those comments (about additional operations to
>>>> consider) to the ticket?
>>>>
>>>
>>> Sure.  Just did that.
>>>
>>>
>>>> relatedly: if we want these atomic ops to use the sequential analogues
>>>> when we're not using the threaded run time system, does that mean
>>>> we need to have a symbol / constant variable exposed in the RTS we link
>>>> in, so that the inline code branches on a linktime constant value / symbol
>>>> (something like "isThreadedRTS:: Bool", )  or some sort of analogue
>>>> thereof?
>>>>
>>>
>>> I think it will take some care to mimic the semantics perfectly.  Why
>>> not just leave the real atomic ops even in non-threaded mode, at least at
>>> first?  Later we can optimize it if we find that people are using
>>> concurrent data structures heavily in non-threaded mode ;-).
>>>
>>>
>>>> one nice thing about doing such, is that if at some point link time
>>>> optimization is added, the branch would go away! On the other hand, it
>>>> could be argued that the cost of the call to the CAS primops in their
>>>> current form isn't that much more expensive than such a branch.
>>>>
>>>
>>> Indeed, I'm much more concerned about performance in the threaded case
>>> and making sure they're correct.
>>>
>>>
>>
>>
>
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