industry-standard single-threaded performance benchmarks absent

By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), February 9, 2010 12:54 pm
Room: Moderated Discussions
Jesper Frimann (jesperfrimann@gmail.com) on 2/9/10 wrote:
>
>If you look at the gains on Nehalem when going from cint
>to cint rate then

.. ok, your numbers do seem to show that, but that seems to
largely be because you are using the results from Sun.

Why do you do that? The Sun results are very different in
base vs peak, and that's where you see the libquantum
breakage too. I consider all those Sun numbers to be
suspect.

So just pick the best 403.gcc number, you'll get

http://www.spec.org/cpu2006/results/res2009q3/cpu2006-20090803-08314.html

which is 32.1/30.2. Now look up the rate matching rate
numbers:

http://www.spec.org/cpu2006/results/res2009q3/cpu2006-20090803-08316.html

and to me it looks like gcc scales to 110/110, which is
just about as well as any of the other benchmarks (just
switch back and forth between them - you get a visual
baseline).

Yeah, it's only a scaling of about 3.6 or so, but that is
not out of line:
- it's almost exactly the same scaling as the
over-all number (37.8 to 139)
- SMT really doesn't help too much on most integer loads
that don't have some big IO footprint
- the single-threaded case gets a Turbo boost from 3.33
to 3.6GHz
- you likely do hit some L3 cache (and perhaps memory)
scaling issues

A factor of about 3.5 is also what I see in some of the
threaded things I use on my 4-core Nehalem too. Sure, I had
hopes for higher, but there you are... (a multi-threaded
"git grep", in case you care).

So I don't think the scaling really proves anything either
way.

Except for libquantum. Now there you have a known
broken benchmark. Look at it scale by less than 2x (228 to
417).

But, yeah, there are benchmarks that scale better than
gcc (but there are others that scale worse), so maybe there
is some autopar going on. Having worked a tiny bit with the
gcc code-base, I have to say that I'm impressed by a
compiler that gets noticeable gains from autopar, though.
It's not like it's a lot of simple array accesses etc.

And as mentioned, the gcc scaling matches the overall
scaling - there is nothing at all out-lier about it.

Linus
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POWER7 SpecParadox2010/02/08 11:05 AM
  POWER7 SpecThu Nguyen2010/02/08 12:58 PM
    POWER7 SpecIan Ameline2010/02/08 09:22 PM
      POWER7 SpecThu Nguyen2010/02/08 11:54 PM
        POWER7 SpecIan Ameline2010/02/09 06:46 AM
          POWER7 SpecLinus Torvalds2010/02/09 07:57 AM
            industry-standard single-threaded performance benchmarks absentMichael S2010/02/09 08:09 AM
              industry-standard single-threaded performance benchmarks absentParadox2010/02/09 08:33 AM
                industry-standard single-threaded performance benchmarks absentMichael S2010/02/09 09:30 AM
                  industry-standard single-threaded performance benchmarks absentParadox2010/02/09 10:52 AM
                    industry-standard single-threaded performance benchmarks absentJesper Frimann2010/02/09 11:33 AM
              industry-standard single-threaded performance benchmarks absentLinus Torvalds2010/02/09 08:48 AM
                industry-standard single-threaded performance benchmarks absentMichael S2010/02/09 09:26 AM
                  industry-standard single-threaded performance benchmarks absentLinus Torvalds2010/02/09 09:58 AM
                    industry-standard single-threaded performance benchmarks absentJesper Frimann2010/02/09 12:17 PM
                      industry-standard single-threaded performance benchmarks absentLinus Torvalds2010/02/09 12:54 PM
                        industry-standard single-threaded performance benchmarks absentJesper Frimann2010/02/09 02:10 PM
                    industry-standard single-threaded performance benchmarks absentParadox2010/02/09 01:22 PM
                industry-standard single-threaded performance benchmarks absentanon2010/02/09 10:21 AM
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