On 4/30/2023 11:33 PM, Inderjit singh via gem5-users wrote:
Any ideas.
Inderjit Singh
On Wed, May 11, 2022 at 10:08 PM Inderjit singh <inderjitsingh.d...@gmail.com
<mailto:inderjitsingh.d...@gmail.com>> wrote:
1. What is the difference between data/tag/response latency?
2. How can I add write latency (for NVM caches) in gem5, any patch?
The tag part of a cache records addresses and access/state bits, typically the
Valid bit (does this entry contain valid information - if not, the entry
should be ignored), Dirty (does the data differ from caches farther away or
the main memory), Shared (are there other copies of this line/block in other
caches), etc.
A cache first takes the address in the request (typically a read or write) and
sees if that addresses occurs is a valid entry in the cache. The amount of
time to do this is the TAG latency.
The DATA latency is the additional time to supply (or update) the data if the
tag matches (a cache hit).
I believe the RESPONSE latency is how long it takes a cache to pass through a
response coming from beyond itself.
As for your question about write latency in NVM caches, I find the question a
little bit ambiguous. I assume you mean volatile caches that cache
information coming from NVM. DATA latency would be the write latency into
such a cache. If you're talking about the internal buffers of an NVM, there
are a slew of parameters in the NVM interface (which combines all the
buffering, etc., with the actual data array). See NVMInterface.py, but also
MemInterface.py. To set such parameters on the command line, you have to do
it for each controller.
This bash code might give you a sense of a way to do it using a script:
# MEMORY parameters
export GEM5_MEMTYPE=${GEM5_MEMTYPE:-NVM_2400_1x64}
export MEM_CHANNELS=${MEM_CHANNELS:-8}
export GEM5_XPARAMS="${GEM5_XPARAMS} --mem-channels=${MEM_CHANNELS}"
export TOTAL_MEM_SIZE_MB=${TOTAL_MEM_SIZE_MB:-512}
## tREAD and tWRITE are guesses ...
## Other values adjusted for 2666 MHz (vs 1200MHz in default gem5)
export MEM_TCK=${MEM_TCK:-0.357ns}
export MEM_TREAD=${MEM_TREAD:-125ns}
export MEM_TWRITE=${MEM_TWRITE:-180ns}
export MEM_TSEND=${MEM_TSEND:-6.28ns}
export MEM_TBURST=${MEM_TBURST:-1.528ns}
export MEM_TWTR=${MEM_TWTR:-0.357ns}
export MEM_TRTW=${MEM_TRTW:-0.357ns}
export MEM_TCS=${MEM_TCS:-0.714ns}
export MEM_DEVICE_SIZE=${MEM_DEVICE_SIZE:=$((TOTAL_MEM_SIZE_MB /
MEM_CHANNELS))MB}
for (( i=0 ; i < $MEM_CHANNELS ; ++i )) ; do
export GEM5_XPARAMS="${GEM5_XPARAMS} --param
system.mem_ctrls[$i].dram.tCK=\'${MEM_TCK}\'"
export GEM5_XPARAMS="${GEM5_XPARAMS} --param
system.mem_ctrls[$i].dram.tREAD=\'${MEM_TREAD}\'"
export GEM5_XPARAMS="${GEM5_XPARAMS} --param
system.mem_ctrls[$i].dram.tWRITE=\'${MEM_TWRITE}\'"
export GEM5_XPARAMS="${GEM5_XPARAMS} --param
system.mem_ctrls[$i].dram.tSEND=\'${MEM_TSEND}\'"
export GEM5_XPARAMS="${GEM5_XPARAMS} --param
system.mem_ctrls[$i].dram.tBURST=\'${MEM_TBURST}\'"
export GEM5_XPARAMS="${GEM5_XPARAMS} --param
system.mem_ctrls[$i].dram.tWTR=\'${MEM_TWTR}\'"
export GEM5_XPARAMS="${GEM5_XPARAMS} --param
system.mem_ctrls[$i].dram.tRTW=\'${MEM_TRTW}\'"
export GEM5_XPARAMS="${GEM5_XPARAMS} --param
system.mem_ctrls[$i].dram.tCS=\'${MEM_TCS}\'"
export GEM5_XPARAMS="${GEM5_XPARAMS} --param
system.mem_ctrls[$i].dram.device_size=\'${MEM_DEVICE_SIZE}\'"
done
This is designed to allow things like MEM_TCK to be set before running this
piece of script, but otherwise to supply the default value 0.357ns (for
example). Once all the above is done, the command line itself must include
${GEM5_XPARAMS} to expand out all of the above. Also, I know its confusing,
but in an NVM only system, the NVM controllers have the name "dram" even
though that are of NVM type!
HTH - Eliot Moss
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