[llvm-commits] [RFC] Add support of RTM from TSX

[Hal Finkel]

----- Original Message -----
> From: "Michael Liao" <michael.liao at intel.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: llvm-commits at cs.uiuc.edu, "Arnamoy Bhattacharyya" <arnamoy at ualberta.ca>
> Sent: Friday, September 21, 2012 1:10:54 PM
> Subject: Re: [llvm-commits] [RFC] Add support of RTM from TSX
> 
> On Fri, 2012-09-21 at 13:00 -0500, Hal Finkel wrote:
> > Michael,
> > 
> > I am happy to see support for transactional memory, and because
> > other
> > architectures also have transactional memory support (like the IBM
> > BG/Q
> > with which I work), I would like to see the interface made slightly
> > more generic. I would like to propose the following interface:
> > 
> > i32 @llvm.tm.begin(i32) - The parameter here is a hint: 0 ==
> > long-running transaction, 1 == short-running transaction (and you
> > can
> > ignore this parameter on x86). The return value is a failure code.
> > We
> > can probably keep Intel's convention: if bit 0 is set then bits
> > 31:24
> > hold the user-defined abort code. If bit 1 is set, then the
> > transaction
> > may succeed upon retry. The exact codes are otherwise
> > target-defined.
> > 
> > void @llvm.tm.end() - End the transactional region
> > 
> > void @llvm.tm.abort(i8) - The i8 is a user-defined abort id
> > 
> > In short, I propose changing the names of your intrinsics and
> > adding
> > the long-running/short-running hint parameter to begin().
> > 
> > Documentation for these would need to be added to the LLVM language
> > reference. For now, the compiler should probably abort if the
> > target
> > does not specifically handle the intrinsics.
> > 
> > Arnamoy, comments?
> 
> That's a really good idea. In fact, I didn't propose that because I
> have
> no idea and detailed information on how different hardware
> transactional
> memory is supported on other architectures, such as IBM's BG/Q and
> Sun's
> Rock.
> 
> I like this proposal and it could simplify the support of C++
> transaction memory onto hardware in LLVM. If no objection, I will
> start
> a separate patch adding these target-independent intrinsics.

Did this happen and I missed it, or have you not gotten to this yet?

Thanks again,
Hal

> 
> Yours
> - Michael
> 
> > 
> >  -Hal
> > 
> > On Fri, 21 Sep 2012 09:57:17 -0700
> > Michael Liao <michael.liao at intel.com> wrote:
> > 
> > > Hi
> > > 
> > > Here's the patch adding RTM support from TSX[1] available in
> > > Haswell[2]. This patch adds 3 intrinsics of RTM, namely xbegin,
> > > xend,
> > > and xabort, which could be used to add hardware support for the
> > > draft
> > > C++ transaction language constructs.
> > > 
> > > Thanks for your review.
> > > - Michael
> > > 
> > > --------------
> > > [1] http://software.intel.com/sites/default/files/319433-014.pdf
> > > [2]
> > > http://software.intel.com/en-us/blogs/2012/02/07/transactional-synchronization-in-haswell
> > 
> > 
> > 
> 
> 
> 

-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory