Ibm HANDBOOK 260 Uživatelský manuál Strana 64

  • Stažení
  • Přidat do mých příruček
  • Tisk
  • Strana
    / 286
  • Tabulka s obsahem
  • KNIHY
  • Hodnocené. / 5. Na základě hodnocení zákazníků
Zobrazit stránku 63
46 RS/6000 43P 7043 Models 150 and 260 Handbook
M (modified) The addressed sector is valid in this cache only. The value in
this sector has been changed in the cache, but the change is
not yet reflected in memory.
E (exclusive) The addressed sector is valid in this cache only. The data is
consistent with system memory.
S (shared) The addressed sector is valid in this cache and at least one
other cache. It is still consistent with system memory.
I (invalid) The addressed sector is not valid in the cache.
2.5.1.8 False Sharing
Figure 17 illustrates false sharing. Here, a whole cache unit of storage (a
cache sector in the case of the IBM SMP systems) is represented.
Figure 17. False Sharing
Suppose processor 1 and processor 2 loaded the same memory address in
their cache. If processor 1 changes only a portion of the cache sector, d1 for
example, the cache consistency logic will invalidate all the sectors in the
processor 2 cache. Then, if processor 2 tries to modify another portion of its
cache sector, d2, for example, which is still invalid since the whole sector is
invalid, a cache miss will occur. This is called false sharing.
Processor 1 Processor 2
Memory
Cache:
d1
d2...
Cache:
d1 d2...
Zobrazit stránku 63
1 2 ... 59 60 61 62 63 64 65 66 67 68 69 ... 285 286

Komentáře k této Příručce

Žádné komentáře