Inclusive L3? Wow

Article: ISSCC 2006: Intel Tulsa
By: Michael S (already5chosen.delete@this.yahoo.com), February 21, 2006 11:03 am
Room: Moderated Discussions
Linus Torvalds (torvalds@osdl.org) on 2/21/06 wrote:
---------------------------
>Michael S (already5chosen@yahoo.com) on 2/21/06 wrote:
>>
>>It should be rather complex to build inclusive cache that
>>has to stay in synch with not one, not two, but SIX inner
>>caches!
>
>Why would that be complex? I think the Intel L2 is already
>inclusive, and so the L3 can totally ignore the L1 I/D side
>entirely. So there are just two inner caches that it needs
>to worry about.
>
>And the L3 would have to be inclusive if you want all the
>coherency logic to be there, and not have to worry about
>snooping the L2. Makes perfect sense to me.
>
>Or am I missing something?
>
>Linus

Yes, you are missing the fact that L2 is not inclusive.

From the latest IA-32 Intel Architecture Optimization Reference Manual:
"Levels in the cache hierarchy are not inclusive. The fact that a line is in level i does not imply that it is also in level i+1. All caches use a pseudo-LRU (least recently used) replacement algorithm."

ftp://download.intel.com/design/Pentium4/manuals/24896612.pdf.
p. 1.20.

Changing L2 cache policy to inclusive would constitute rather big change in the Netburst microarchitecture hardly justifiable by needs of the single low-volume member of the family, especially taking into account that it is most likely the last member.



< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
Intel Tulsa Coverage from ISSCCDavid Kanter2006/02/21 02:45 AM
  Intel Tulsa Coverage from ISSCCAlberto2006/02/21 04:43 AM
    Intel Tulsa Coverage from ISSCCPaul DeMone2006/02/21 06:52 AM
  Inclusive L3? WowMichael S2006/02/21 04:51 AM
    Inclusive L3? WowWouter Tinus2006/02/21 07:06 AM
      Inclusive L3? WowMichael S2006/02/21 08:20 AM
        Inclusive L3? Wowslim2006/02/21 11:40 AM
    It is?anonymous2006/02/21 09:57 AM
    Inclusive L3? WowLinus Torvalds2006/02/21 10:10 AM
      Inclusive L3? WowMichael S2006/02/21 11:03 AM
        Inclusive L3? WowLinus Torvalds2006/02/21 11:52 AM
          Inclusive L3? WowEric Bron2006/02/22 06:39 AM
            Inclusive L3David Kanter2006/02/22 12:16 PM
              Inclusive L3Eric Bron2006/02/22 01:00 PM
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