Re: [Gems-users] Does gems (ruby) model the DMA operations now?

[Muhammad abid Mughal <mabidm_pieas@xxxxxxxxx>]

hi

I do know that Ruby does not support DMA requests even in gems-2.1. It just filters them out via SimicsDriver::isunhandledtransaction(), so its not possible for DMA requests to invalidate the corresponding cache blocks in L1/L2 caches[i am wondering that DMA accesses I/O blocks and Ultrasparc processor does not allow caching of i/o blocks, so no question of invalidating corresponding L1$/L2$ blocks.am i right?] 

Regards,

Muhammad abid

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From: Sitos Lin <sitos.lin@xxxxxxxxx>
To: gems-users@xxxxxxxxxxx
Sent: Friday, December 18, 2009 11:24:41
Subject: [Gems-users] Does gems (ruby) model the DMA operations now?

Hello all:
  I want to use gems (ruby) to capture the memory access trace.
However, I am wondering if gems models the DMA operations. In the
paper, it says "Also, Ruby does not model the memory system traffic
due to direct memory access (DMA) operations or memory-mapped I/O
loads and stores." However, gems is now version 2.1. Does gems model
the DMA operations now?
  Besides that, if the memory system traffic of DMA operations are not
modeled, I want to know if DMA operations invalidate the correspondent
cache blocks in L1/L2 caches. Since the values of memory have been
changed by DMA (read) operations, the cache blocks should be
invalidated and the following cache accesses to these lines should be
miss. I have tried to test gems by two simple program. However, the
results are not consistent to my knowledge. The program with
additional DMAs causes less cache misses than another one without DMA
operation.
  If gems can not model the features mentioned above, I will try other
approaches.
Best regards,
  Sitos
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