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Re: [PATCH 3/6] Use XEND when a lock is busy in an elision attempt.
- From: Andi Kleen <andi at firstfloor dot org>
- To: Torvald Riegel <triegel at redhat dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Wed, 11 Sep 2013 16:04:17 -0700
- Subject: Re: [PATCH 3/6] Use XEND when a lock is busy in an elision attempt.
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- References: <20130902075228 dot GA4792 at linux dot vnet dot ibm dot com> <20130902080214 dot GC4997 at linux dot vnet dot ibm dot com> <87k3izdjn8 dot fsf at tassilo dot jf dot intel dot com> <20130903082522 dot GA16924 at linux dot vnet dot ibm dot com> <87a9jtpl2j dot fsf at tassilo dot jf dot intel dot com> <1378915322 dot 3196 dot 14459 dot camel at triegel dot csb>
Torvald Riegel <triegel@redhat.com> writes:
>> Since z transactions and TSX are somewhat different I think it's
>> expected that the elision code for both diverges.
>
> While this might eventually be true, it is something that we should
> really try to avoid. Andi, you complained about the multiple
> arch-specific versions of some of the pthreads code in the past, and
> forking the elision code without need would be exactly the same problem.
>
> We should try really hard to keep this generic as much as possible.
> Ideally, I'd like both of you to sit down and flesh out the adaptation
> in more detail, and look for the commonalities there.
It needs more experimentation first. I consider the current algorithm
preliminary. We already have a better set of skip counts now
(I had an intern working on this this summer), but there
is still some more work needed to evaluate more options.
I also consider this to be an area where more research would make sense.
But again TSX is different from zSeries.
For example the micro benchmarks Dominik was working with earlier
behaved very different.
>> We reserved some fixed values for abort codes in the optimization guide
>> (you can see that as a kind of ABI)
>
> Is this an official "Intel-blessed" document?
It's Intel authored.
> Can you post the link?
http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf
12.4.5
> Who does this apply to?
Everyone who wants to follow it. At least all my code and pretty much
all of the examples use this convention.
-Andi
--
ak@linux.intel.com -- Speaking for myself only