>>>>> "tbisson" == tbisson <tbisson@soe.ucsc.edu> writes: tbisson> Yeah, several sources I've seen give that equation. Ok. tbisson> Question: cache stores "physical page addresses" (on P4's), right? tbisson> I have a 512K cache w/64B lines and is 8-way. Nope, the cache (the one that is 512K) stores the memory content, not memory addresses. The TLB stores addresses. tbisson> If so, then cache_size/page_size = number of colors for a tbisson> direct mapped. For example 4096K cache size and 4K pages, tbisson> then there are 1024 colors or physical_page_address_indexes tbisson> that won't conflict. Thus, if we have a process we want to tbisson> improve performance with, we assign it physical pages tbisson> contigouslly from tbisson> "phy_page_num mod num_colors =0" to "phy_page_num mod tbisson> num_colors = num_colors -1" tbisson> so that it uses all the cache. Right. With set-associative caches page coloring helps allocating pages whose lines cache to different sets. Let for concreteness use 32-bit addresses, 512K, 8-way set-associative cache, 64-byte cache line size. The address is split like <tag:16 set:10 byte:6>. The ``set'' field selects one of 1024 == 512K / (8 * 64) sets and the cache line goes to either of the 8 ways of the set. The page allocation affects the upper 4 bits of the ``set'' field. If two pages has these 4 bit different (== having different color), the lines in them cache to different sets, thus do not conflict. tbisson> If the L2 cache stores "physical page addresses", what use tbisson> would the cache be without a TLB? It seems like they are tbisson> dependent upon each other for performacne? Nope, they are independent. The cache caches ordinary memory, the TLBs cache address translation results. Tim> num_colors = cache_size/(associativity*page_size). >> Page coloring is made to improve the utilization of the TLBs. Actually, that statement of mine is NOT true. Even more with fully-associative TLBs. ~velco -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
