Why the platform focus?

Article: Tukwila Update
By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), February 5, 2009 11:03 am
Room: Moderated Discussions
someone (someone@somewhere.com) on 2/5/09 wrote:
>
>According to this study half of SPECint2006 programs have
>average core working sets exceeding 16 MB and nearly 20%
>exceed 32 MB:

Oh, you need more memory than the caches have, but I really
doubt that SpecInt has become that sensitive to the
cache size. At some point the numbers were along the lines
of "max 10% improvement from tripling the cache".

So no, SpecInt2006 certainly won't fit in the cache,
but with a larger cache you do capture a hell of a lot
of it. Things have a lot of locality. From a cache size
standpoint, the interesting part is the momentary working
set.

>The maximum cache one core/thread can use is 6 MB in C2D,
>8 MB in i7, and 12 MB in Itanium.

Actually, the number I quoted for Itanium was for the
18MB L3 cache (does that make it 9M per core?). Why?

Because that's the highest performance result I found, due
most likely to the 1.66GHz (rather than 1.6GHz) sku.

That should already tell you something: it's not nearly
as cache sensitive as it is frequency-sensitive. The
smaller cache wins, just because it runs a tiny bit
faster.

Now, it's hard to do cache sensitivity analysis on the
SpecInt2006 numbers, exactly because there are different
frequencies, and they are submitted by different vendors
at different times. But go look, and you'll see that the
difference between the 18MB and 24MB sku's for the cases
when the same vendor reported numbers at the same time
are basically zero.

Of course, maybe the smaller-cache one had a worse memory
subsystem, and they just happened to cancel out, so it
proves nothing, but I think it's more likely that 16MB
cache is just "enough" that platform effects aren't that
big at least on SpecInt. Yes, even 2006.

(And obviously things change if you have much less cache.
The difference between 1MB and 2M is going to be quite big.
But when everybody involved has 8M+ of cache, what matters
most is how fast the cache is - at different levels -
and the core itself. Not so much the platform outside the
L3).

Linus
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TopicPosted ByDate
Tukwila Update - article onlineDavid Kanter2009/02/04 11:03 PM
  Tukwila Update - article onlineDan2009/02/05 02:17 AM
    Tukwila Update - article onlineJoe Chang2009/02/05 08:16 AM
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            Great. Finally hard numbersMichael S2009/02/06 03:46 AM
            Tukwila Update - article onlinelubemark2009/02/06 04:54 AM
              Tukwila Update - article onlinePhil2009/02/06 06:29 AM
                Tukwila Update - article onlineRagingDragon2009/02/07 02:39 PM
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            Tukwila Update - article onlinesomeone2009/02/06 06:18 AM
              Tukwila Update - article onlinePhil2009/02/06 06:47 AM
                Tukwila Update - article onlinesomeone2009/02/06 07:17 AM
                Tukwila Update - article onlineRagingDragon2009/02/07 02:51 PM
              Tukwila Update - article onlineLinus Torvalds2009/02/06 07:37 AM
                Tukwila Update - article onlinesomeone2009/02/06 08:19 AM
                Tukwila Update - article onlinesavantu2009/02/06 09:19 AM
                  Tukwila Update - article onlineLinus Torvalds2009/02/06 09:40 AM
                    Tukwila Update - article onlinesavantu2009/02/06 10:00 AM
              Tukwila Update - article onlinePhil2009/02/09 03:54 AM
                Tukwila Update - article onlineDoug Siebert2009/02/09 09:40 PM
                  Tukwila Update - article onlineJouni Osmala2009/02/10 12:03 AM
                  Tukwila Update - article onlinesomeone2009/02/10 05:15 AM
                Tukwila Update - article onlineslacker2009/02/10 05:22 PM
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    Tukwila Update - article onlineDavid Kanter2009/02/05 03:55 PM
    Tukwila Update - article onlinesomeone2009/02/05 04:47 PM
      Tukwila Update - article onlineanon2009/02/05 09:16 PM
        Tukwila Update - article onlineRagingDragon2009/02/05 09:27 PM
        Tukwila Update - article onlinesomeone2009/02/06 06:32 AM
          Tukwila Update - article onlineanon2009/02/06 08:25 AM
            Tukwila Update - article onlinesomeone2009/02/06 08:40 AM
  POWER6 memory bandwidthMichael S2009/02/05 02:30 AM
    POWER6 memory bandwidthsomeone2009/02/05 06:00 AM
      POWER6 memory bandwidthMichael S2009/02/05 06:36 AM
      POWER6 interconnectconfused2009/02/05 09:50 AM
        POWER6 interconnectfoobar2009/02/05 01:12 PM
    POWER6 memory bandwidthWes Felter2009/02/05 11:57 AM
    POWER6 memory bandwidthJesper Frimann2009/02/09 10:54 PM
      POWER6 memory bandwidthMichael S2009/02/10 06:21 AM
  Why the platform focus?Linus Torvalds2009/02/05 07:40 AM
    Why the platform focus?savantu2009/02/05 07:50 AM
      Why the platform focus?Vincent Diepeveen2009/02/05 08:29 AM
        Why the platform focus?savantu2009/02/05 09:34 PM
          Why the platform focus?Vincent Diepeveen2009/02/05 10:09 PM
          Why the platform focus?Phil2009/02/06 12:10 AM
            Why the platform focus?savantu2009/02/06 12:50 AM
              Why the platform focus?Phil2009/02/06 06:09 AM
                Why the platform focus?savantu2009/02/06 09:08 AM
                Why the platform focus?someone2009/02/06 09:21 AM
                  Why the platform focus?mpx2009/02/06 01:04 PM
                    Why the platform focus?someone2009/02/06 01:16 PM
                Why the platform focus?RagingDragon2009/02/07 03:16 PM
                Why the platform focus?mas2009/02/25 07:28 AM
              itanium bigger than entire car industryVincent Diepeveen2009/02/06 06:12 AM
                itanium bigger than entire car industryDevon Welles2009/02/06 06:51 AM
                  itanium bigger than entire car industryVincent Diepeveen2009/02/06 09:41 AM
                  itanium bigger than entire car industryDean Kent2009/02/06 06:56 PM
                    Unit sales is meaningless when ASP grows fastersomeone2009/02/07 08:38 AM
                      Unit sales is meaningless when ASP grows fasterDean Kent2009/02/07 02:10 PM
                        Unit sales is meaningless when ASP grows fasterRagingDragon2009/02/07 03:34 PM
                    itanium bigger than entire car industryVincent Diepeveen2009/02/08 04:35 AM
                itanium bigger than entire car industryRagingDragon2009/02/07 03:40 PM
            Why the platform focus?Vincent Diepeveen2009/02/06 06:47 AM
      Yes it doesm performance mattersbob2009/02/05 09:51 AM
        Yes it doesm performance mattersVenki2009/02/05 10:06 AM
      Why the platform focus?Doug Siebert2009/02/06 12:07 AM
        Why the platform focus?savantu2009/02/06 01:00 AM
    Why the platform focus?someone2009/02/05 09:49 AM
      Why the platform focus?Linus Torvalds2009/02/05 11:03 AM
        Why the platform focus?Default2009/02/05 12:29 PM
          Why the platform focus?anon2009/02/05 01:08 PM
        Why the platform focus?someone2009/02/05 01:24 PM
          Why the platform focus?Linus Torvalds2009/02/05 02:30 PM
    Why the platform focus?Paradox2009/02/05 10:22 AM
    Why the platform focus?slacker2009/02/05 12:41 PM
      Why the platform focus?RagingDragon2009/02/05 09:57 PM
      Why the platform focus?Michael S2009/02/06 05:11 AM
        Why the platform focus?slacker2009/02/06 12:58 PM
          Why the platform focus?Michael S2009/02/08 01:24 AM
            Why the platform focus?someone2009/02/08 08:38 AM
              Why the platform focus?David Kanter2009/02/08 03:27 PM
                Why the platform focus?someone2009/02/08 06:26 PM
                  Why the platform focus?savantu2009/02/08 11:35 PM
          Why the platform focus?someone2009/02/08 08:53 AM
    All x86 SpecInt scores are useless due to autopar (NT)Michael S2009/02/05 02:15 PM
      Auto parallelizationDavid Kanter2009/02/05 05:17 PM
      All x86 SpecInt scores are useless due to autopar (NT)Paradox2009/02/06 07:47 AM
    Why the platform focus?David Kanter2009/02/05 03:49 PM
    Why the platform focus?David Kanter2009/02/06 12:09 AM
      Why the platform focus?Linus Torvalds2009/02/06 07:14 AM
        Why the platform focus?savantu2009/02/06 09:37 AM
          Why the platform focus?Linus Torvalds2009/02/06 11:49 AM
            Why the platform focus?Linus Torvalds2009/02/06 12:09 PM
            Intel puts its money where its mouth issomeone2009/02/06 01:08 PM
              Intel puts its money where its mouth isRagingDragon2009/02/07 05:01 PM
                Intel puts its money where its mouth issomeone2009/02/08 01:24 PM
                  mission-criticalMichael S2009/02/08 04:06 PM
                    mission-criticalmpx2009/02/09 01:30 AM
                      mission-criticalrwessel2009/02/09 02:23 PM
                    mission-criticalanon2009/02/09 02:55 AM
                    mission-criticalEduardoS2009/02/09 04:17 PM
                      mission-criticalDean Kent2009/02/09 07:11 PM
                        mission-criticalMichael S2009/02/10 04:20 AM
                          mission-criticalDean Kent2009/02/10 06:26 AM
                            mission-criticalMichael S2009/02/10 07:01 AM
                              mission-criticalDean Kent2009/02/10 12:36 PM
                            mission-criticalsomeone2009/02/10 08:05 AM
                              mission-criticalDean Kent2009/02/10 12:22 PM
                                mission-criticalZt2009/02/22 03:54 PM
                          mission-criticalanon2009/02/10 09:41 PM
                        mission-criticalEduardoS2009/02/10 12:46 PM
                          mission-criticalDean Kent2009/02/10 01:31 PM
                        mission-criticalslacker2009/02/10 06:30 PM
                    mission-criticalVincent Diepeveen2009/02/18 06:20 AM
                  Mission criticalmpx2009/02/09 12:00 AM
            Why the platform focus?savantu2009/02/07 12:15 AM
              Sun and x86 server differentiationDavid Kanter2009/02/07 12:34 AM
                Sun and x86 server differentiationmax2009/02/07 02:30 AM
                Sun and x86 server differentiationsomeone2009/02/07 09:19 AM
                  Sun and x86 server differentiationLinus Torvalds2009/02/07 09:44 AM
                Sun and x86 server differentiationRagingDragon2009/02/07 05:09 PM
                  Sun and x86 server differentiationMichael S2009/02/08 04:05 AM
                    Sun and x86 server differentiationRagingDragon2009/02/09 11:03 PM
                    Sun and x86 server differentiationJesper Frimann2009/02/09 11:51 PM
                      Sun and x86 server differentiationAlex Jones2009/02/10 12:43 PM
            Why the platform focus?bob2009/02/08 03:51 AM
              Why the platform focus?someone2009/02/08 08:23 AM
          missing the big pictureAM2009/02/18 05:43 AM
            missing the big pictureMichael S2009/02/18 07:42 AM
              missing the big pictureAM2009/02/18 08:03 AM
        Why the platform focus?mpx2009/02/06 11:47 AM
          Itanium - slowest and most obsolete server CPU family in the world, NOW.mpx2009/02/06 03:48 PM
            Itanium - slowest and most obsolete server CPU family in the world, NOW.Paul2009/02/07 01:56 PM
              z series?Michael S2009/02/07 02:12 PM
              Itanium - slowest and most obsolete server CPU family in the world, NOW.someone else2009/02/24 03:37 AM
                Itanium - slowest and most obsolete server CPU family in the world, NOW.EduardoS2009/02/24 05:55 AM
                  Itanium - slowest and most obsolete server CPU family in the world, NOW.someone else2009/02/25 12:55 AM
                    Itanium - slowest and most obsolete server CPU family in the world, NOW.Michael S2009/02/25 01:27 AM
          Why the platform focus?RagingDragon2009/02/07 05:18 PM
            Why the platform focus?Paul2009/02/08 12:10 PM
              Why the platform focus?Jukka Larja2009/02/08 10:04 PM
        Why the platform focus?slacker2009/02/06 01:10 PM
          Why the platform focus?Linus Torvalds2009/02/06 01:40 PM
            Why the platform focus?savantu2009/02/06 01:51 PM
            Why the platform focus?someone2009/02/06 01:58 PM
              Why the platform focus?Linus Torvalds2009/02/07 08:26 AM
                Why the platform focus?someone2009/02/07 09:10 AM
                  Why the platform focus?Linus Torvalds2009/02/07 09:40 AM
                    Why the platform focus?someone2009/02/07 11:24 AM
                      Why the platform focus?Doug Siebert2009/02/07 11:32 PM
                        Why the platform focus?max2009/02/08 03:57 AM
                          Why the platform focus?Michael S2009/02/08 04:20 AM
                        Why the platform focus?someone2009/02/08 08:15 AM
                          Why the platform focus?Doug Siebert2009/02/08 10:36 PM
                      Why the platform focus?hobold2009/02/09 04:49 AM
                Why the platform focus?anon2009/02/24 12:57 AM
                  Why the platform focus?Linus Torvalds2009/02/24 08:45 AM
                    Why the platform focus?savantu2009/02/24 11:30 AM
                      Why the platform focus?slacker2009/02/24 12:51 PM
                        Why the platform focus?savantu2009/02/24 11:04 PM
                          Why the platform focus?Michael S2009/02/25 01:34 AM
                          Why the platform focus?anon2009/02/25 09:17 AM
                      Why the platform focus?max2009/02/25 10:15 AM
                    Why the platform focus?someone2009/02/24 04:43 PM
                      Why the platform focus?Doug Siebert2009/02/24 07:26 PM
                        Why the platform focus?Howard Chu2009/02/25 02:07 AM
                          Why the platform focus?someone2009/02/25 05:48 AM
                        Why the platform focus?someone2009/02/25 05:41 AM
                          Why the platform focus?Linus Torvalds2009/02/25 08:17 AM
                            Why the platform focus?someone2009/02/25 08:55 AM
                              has anyone seen Tukwila silicon?anon2009/02/25 09:38 AM
                              Why the platform focus?Linus Torvalds2009/02/25 10:05 AM
                                Why the platform focus?slacker2009/02/25 12:11 PM
                                Why the platform focus?a reader2009/02/26 08:11 PM
                                  Why the platform focus?rcf2009/02/27 12:32 PM
                                    Why the platform focus?max2009/02/27 01:11 PM
                                      Why the platform focus?rcf2009/02/27 02:50 PM
                            Why the platform focus?Vincent Diepeveen2009/02/25 03:30 PM
                            $40M sale to $16M companybob2009/02/25 07:25 PM
                              $40M sale to $16M companyRichard Cownie2009/02/26 11:21 AM
                  Why the platform focus?anonymous2009/02/24 10:52 AM
                    Why the platform focus?savantu2009/02/24 11:20 AM
                      Why the platform focus?anonymous2009/02/24 02:31 PM
                        Why the platform focus?savantu2009/02/24 11:05 PM
                        Why the platform focus?someone else2009/02/25 12:04 AM
                          Why the platform focus?Michael S2009/02/25 12:42 AM
                            Put me down for $500 that Poulson doesn't arrive earlier than Q4/2011 (NT)slacker2009/02/25 11:39 AM
                        Why the platform focus?someone2009/02/25 05:54 AM
                          Why the platform focus?anonymous2009/02/25 08:46 AM
                            Why the platform focus?someone2009/02/25 09:22 AM
                            Why the platform focus?anon2009/02/25 10:01 AM
                              Why the platform focus?anonymous2009/02/25 10:54 AM
                  Why the platform focus?mpx2009/02/24 01:11 PM
                    Why the platform focus?anon2009/02/24 07:57 PM
                      Why the platform focus?Doug Siebert2009/02/24 09:04 PM
                        Why the platform focus?anon2009/02/24 09:46 PM
                          Why the platform focus?Doug Siebert2009/02/25 04:13 PM
                            Why the platform focus?anon2009/02/25 07:53 PM
                              Why the platform focus?bob2009/02/25 08:00 PM
                                Please try to keep up (NT)anon2009/02/25 08:49 PM
                              Why the platform focus?Doug Siebert2009/02/25 11:09 PM
                                Why the platform focus?anon2009/02/26 12:12 AM
                                Why the platform focus?Michael S2009/02/26 01:16 AM
                                  Why the platform focus?James2009/02/26 05:09 AM
                                    sufficiently intimate with the OSMichael S2009/02/26 05:29 AM
                                      sufficiently intimate with the OSanon2009/02/27 12:01 AM
                                      sufficiently intimate with the OSHoward Chu2009/02/27 12:37 AM
                      Why the platform focus?Michael S2009/02/25 01:02 AM
                        Why the platform focus?anon2009/02/25 02:07 AM
              Why the platform focus?anon2009/02/07 12:18 PM
                Why the platform focus?Vincent Diepeveen2009/02/08 09:16 AM
                Why the platform focus?anon2009/02/25 06:40 AM
                  Intels financial statusVincent Diepeveen2009/02/25 11:02 AM
                Why the platform focus?someone2009/02/25 06:54 AM
      Why the platform focus?Vincent Diepeveen2009/02/06 07:20 AM
        Why the platform focus?Default2009/02/06 08:57 AM
          Why the platform focus?Vincent Diepeveen2009/02/06 09:59 AM
          Why the platform focus?RagingDragon2009/02/07 05:43 PM
  Tukwila Update - article onlineVincent Diepeveen2009/02/05 08:11 AM
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