TAG_LATENCY isn't used in MOESI_CMP_directory (at least not that I can see in my install using MOESI_CMP_directory_m). The L1_REQUEST_LATENCY should be the non-network time it takes an L1 cache to request a line from L2, and the L2_REQUEST_LATENCY should be the non-network latency needed to issue a request to an L1 (or possibly an L2 I think, but I could be wrong). I'm not 100% positive about this, but I want to say this is what I figured out one day on the MOESI_CMP_directory protocol.
To really understand what your results are showing, you need to give more details of the simulation. How many cycles did you execute each one for, how many cpus were there, how many instructions did each cpu execute, etc. Also, what were you testing, was it a multithreaded application, a single threaded one, and what cpu was each thread executing on.
Phil
On Apr 20, 2010, at 2:24 PM, Dan Gibson wrote:
1. In theory, the two latencies represent the time required to respond with data (response) versus the time to respond with a control message (request), which is in theory related to tag/data array organization. In practice, many protocols simply use one latency and ignore the others. Hence, my previous post stads: grep through the protocol to find out which ones are used.
2. Are you running for a fixed number of instructions? If so, it is likely that one or more processor is spinning, completing instructions very quickly. Other non-spinning processors spend more time waiting on memory (because you have lengthened cache latency), which reduces the total number of misses.
Regards, Dan
On Tue, Apr 20, 2010 at 2:18 PM, Mark Samuelson <msamuelson@xxxxxxxx> wrote:
I meant what does response latency and the request latency measure? Is
the request latency the time between when a request is sent to a cache
and the time the cache receives it? Is the response latency the time
it takes to send a response from the cache? Shouldn't those be the
same thing?
Increasing the latency and the cache misses halved from 100000 to
50000. All subsequent runs at either latency setting are very close to
these values (within one or two misses).
On 4/20/2010 1:06 PM, Dan Gibson wrote:
1. You can grep through a protocol's .sm files to find out
what latencies it uses.
2. You can never trust a comparison of only one run. When simulating
multiprocessors, small timing perturbations can cause threads to take a
different path. This is why we typically use many (~10) runs per
configuration to achieve a reasonable 95% confidence interval. See
Alameldeen and Wood: http://www.cs.wisc.edu/multifacet/papers/hpca03_variability.pdf
Regards,
Dan
On Tue, Apr 20, 2010 at 1:03 PM, Mark
Samuelson <msamuelson@xxxxxxxx>
wrote:
We
are using MOESI_CMP_directory. And yes, we checked to make sure
everything else was the same.
Philip Garcia wrote:
what protocol are you using, I know many of these
parameters aren't used under some protocols, and even if they are,
increasing them shouldn't reduce runtime, are you sure you're running
on the same checkpoint, and that nothing else changed?
Phil
On Apr 20, 2010, at 12:37 PM, Mark Samuelson wrote:
We
are running a simple program and found increasing the L2 request and
response latencies improved both the cache miss rate and the overall
runtime.
Does anyone know what the difference between the request, response, and
tag latencies are?
-- http://www.cs.wisc.edu/~gibson [esc]:wq!
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