[PATCH] Handle abortTransaction with RTM

[Richard Henderson <rth at redhat dot com>]

On 2012-11-08 15:32, Torvald Riegel wrote:
> On Thu, 2012-11-08 at 15:38 +0000, Lai, Konrad wrote:
>> The xabort argument is the only "escape" currently allowed in RTM. So it is not possible to use a separate Boolean in memory.
> 
> No, that's not what I meant.  The boolean would be used in libitm's
> htm_abort(), which the architecture-specific code (eg,
> config/x86/target.h) would then change into whatever the particular HTM
> uses as abort reasons (eg, true would become 0xff).  That's just to keep
> as much of libitm portable as possible, nothing more.
> 
>> [Roman just posted an example in http://software.intel.com/en-us/blogs/2012/11/06/exploring-intel-transactional-synchronization-extensions-with-intel-software ]
>>
>> I don't know "any" large code that uses cancel. Someone claim there is one in STAMP, and one got speed up if it was removed. I think this discussion potentially explains why.
> 
> The abort in STAMP is bogus.  They didn't instrument all of the code (if
> you use the manual instrumentation), and the abort is just there to
> "catch" race conditions and other inconsistencies.
> 
> My suggestions for next steps are to move the begin stuff to assembly.
> After that, we can go for the abort branch, if removing it really makes
> a non-negligible performance difference.

I believe this is the sort of patch that Torvald was talking about
for handling abortTransaction with RTM.

Andi, can you please test?


r~

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