Hi Amin, Tao,
My short answer is in fact a question rather than an answer: What accuracy are
you referring to?
The long answer: The SimpleDRAM model is capturing the behaviour of the memory
controller rather than the DRAM itself (although the latter of course affects
the former). Thus, the accuracy that the model aims to deliver is with respect
to the behaviour as seen from the system. Certain DRAM parameters are indeed
left out at the moment, and you could argue that this affects the precision of
the modelling, but I would suggest the link to accuracy is not so clear. Having
a more precise model of the DRAM does not necessarily give a more accurate
model of the impact on the system. Accuracy vs precision :-). More important
than a precise DRAM model is the queuing and arbitration of the controller. The
low-power states are indeed important to model, especially from a power point
of view, and this would be a great addition to the model.
Another important question is: what do you want it to be accurate with respect
to? If accuracy means correlation with real silicon, then what SoC/platform? To
the best of my knowledge, neither the SimpleDRAM model, nor DRAMSim1/2 has been
compared to an actual memory controller implementation (only the DRAM side of
things for the latter). Such a comparison would also be of value.
I hope that provides you with all the information you need in terms of making a
choice. Other benefits of the SimpleDRAM models (DDR3, LPDDR2 etc) is that they
are fast and very configurable.
Andreas
From: Tao Zhang <[email protected]<mailto:[email protected]>>
Reply-To: gem5 users mailing list
<[email protected]<mailto:[email protected]>>
Date: Thursday, 9 May 2013 04:17
To: 'gem5 users mailing list' <[email protected]<mailto:[email protected]>>
Subject: Re: [gem5-users] SimpleDRAM accuracy
Hi Amin,
You can refer to Andreas’s clarification for the similar concern.
http://www.mail-archive.com/[email protected]/msg07444.html.
As he said, you can use SimpleDDR3 or LPDDR2_S4 to capture a more accurate
memory timing behavior. Compared to the simplest memory model that only assigns
constant (average) latency to each memory request, the SimpleDRAM indeed has
“good-enough accuracy”. If you are working on the main memory part, then the
good starting point is SimpleDDR3 rather than SimpleDRAM as the former has even
better accuracy.
In my case, I didn’t compare SimpleDRAM or SimpleDDR3 with DRAMSim2. Since
SimpleDDR3 has no timing parameter like tWR and tRRD, nor low power mode (tPD,
tXP…), it has some performance difference from the real case. Again, you should
decide whether the accuracy is good enough for your work.
On the other hand, we really compared our own simulator NVMain
(http://www.nvmain.org ) with DRAMSim2. We got similar performance as the
validation of our tool. If you are interested, you can ask for the source code
on the website.
-Tao
From: [email protected]<mailto:[email protected]>
[mailto:[email protected]] On Behalf Of Amin Farmahini
Sent: Wednesday, May 08, 2013 9:21 PM
To: gem5 users mailing list
Subject: [gem5-users] SimpleDRAM accuracy
Hi,
Comparing SimpleDRAM model and DRAMSim2 model, I was wondering how timing
accurate SimpleDRAM is for memory-intensive applications? This might be a
question for Andreas and Tao and I know this is a very general question, but
any thoughts on this would be appreciated. Andreas mentioned that SimpleDRAM
provides "good-enough accuracy." More information on the accuracy would be
great.
I realized some detailed parameters such as FAW are integrated into SimpleDRAM,
and some other like RRD are left out. So my next question is whether there are
any plans to model more detailed DRAM behavior?
Thanks,
Amin
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