Hi Shan, See below. We will try to get the state diagram out soon.
Regards, -Tom Wenisch ---------- Forwarded message ---------- List-Post: [email protected] Date: Tue, 25 Oct 2005 13:53:49 -0400 (EDT) From: Jared C. Smolens To: [email protected] Subject: Re: [Simflex] CMP cache coherence protocol question Excerpts From "shan" <[email protected]>: [Simflex] CMP cache coherence proto: "shan" <[email protected]> >Hi Tom, > Is there some document or something explaining the cache coherence for > CMP in the SimFlex? I know the general MOSI protocol and I read the >PiranhaCache-Controller files, but maybe because I am not very familiar >with the CMP and cache coherence, I still do not understand this module >very well. I am preparing the state diagram for distribution. Stay tuned. > The document said the SimFlex CMP has private L1 and shared L2. Does >that mean there are only one L2 and only one directory shared by all >cores? Yes. We maintain a logical directory at a single, shared L2 in CMPFlex. The directory covers all lines in the CMP core. >Is the M-E-S-I states shared by all cores? The coherence states (including transient states) are maintained in a directory structure at the shared L2. The L1 caches have the same states as in DSMFlex (permutations of Valid, Modifiable, and Dirty bits). > Does the L1 cache in CMP need to be configured somehow different from > that in the Uni-processor scenario? Yes, there is one difference from the Uhiprocessor/DSMFlex configurations: the EvictClean option is set to true in CMPFlex. This option causes clean lines to be sent to the L2, instead of being silently dropped on replacement. This models Piranha's use of the shared cache as a large "victim cache" for L1 replacements. >I didn't find the difference in the >wiring.cpp. However, shouldn't the L1 cache at least be write-through >instead of write-back? The private caches are still write-back, but both clean and dirty lines are written back to the shared cache on replacement. > Sorry to take your time with so many questions. > >Thanks >Shan Jared Smolens ----------- Electrical and Computer Engineering www.rabidpenguin.org ------------- Carnegie Mellon University
