Cliff Click Jr. on Azul's HTM

By: Paul A. Clayton (paaronclayton.delete@this.gmail.com), September 24, 2010 1:19 pm
Room: Moderated Discussions
David Kanter (dkanter@realworldtech.com) on 9/24/10 wrote:
---------------------------
[snip]
>I think Azul had something much simpler than TM. I think they are now porting
>to nehalem-ex, so they clearly don't need TM for some of their stuff.

http://www.azulsystems.com/blog/cliff-click/2009-02-25-and-now-some-hardware-transactional-memory-comments

Some interesting quotes:
"Software heuristics determine when to try the HTM (uncontended locks are much cheaper using a cache-hitting CAS)"

"we had lots of teething problems with the software heuristic that used to cause 10-20% slowdowns due to endless fail/retry loops"

"HTM failure appears to nearly always be due to conflict and not capacity"

"Why make the code XTN-friendly when they can make it lock-friendly as well, and have it run fine on all gear (and not just HTM-enabled gear)?"

"It's not the case that they need to write some uber-hard-to-maintain code to get performance. Instead it's the case that they have no clue which locks need to be "cracked" to get a speedup, and once that's pointed out the fixes are generally straightforward."

(A bit discouraging that TM might not be a generally
significant win even if universally supported.)


Paul A. Clayton
just a technophile
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          Transactional memory Paul A. Clayton2010/09/23 06:30 AM
            Transactional memory Linus Torvalds2010/09/23 07:01 AM
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                      'dynamic fallback'?Linus Torvalds2010/09/25 12:23 PM
                        'dynamic fallback'?blaine2010/09/25 01:16 PM
                Cliff Click Jr. on Azul's HTMPaul A. Clayton2010/09/24 01:19 PM
              Transactional memory Foo_2010/09/24 02:08 AM
    T3 announcedblaine2010/09/21 10:43 AM
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