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

[Muhammad abid Mughal <mabidm_pieas@xxxxxxxxx>]

Hi,

 Is gems aware this? yes

 If you are using Simics and Ruby then for every memory operation(ie ld/st/atomic/ifetch/prefetch/dma/io, etc)  simics calls this function

    SimicsDriver::makeRequest() and this function filters out all unsupported operations(ie i/o , DMA,cache flush, prefetch) via  SimicsDriver::isUnhandledTransaction(). so this way DMA/ io operations are not passed to Ruby and not cached in any caches.

Do you have any idea about how to know where are the I/O blocks?

you need to make some changes to this function SimicsDriver::isUnhandledTransaction(). whenever memory is accessed by DMA or I/O device this 

IS_DEV_MEM_OP(mem_trans->s.ini_type) returns true and you can use 'mem_trans' arg to do some profiling

Hope it helps

Regards,

Muhammad abid

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From: Sitos Lin <sitos.lin@xxxxxxxxx>
To: Gems Users <gems-users@xxxxxxxxxxx>
Sent: Saturday, December 19, 2009 14:52:44
Subject: Re: [Gems-users] Does gems (ruby) model the DMA operations now?

Hello:
  You said that " DMA accesses I/O blocks and Ultrasparc processor
does not allow caching of I/O blocks". Is gems aware this? If the I/O
blocks are uncacheable, maybe I can gather the memory accesses
correspondent to DMA operations by monitoring the memory accesses
belong to I/O blocks by knowing the memory range of I/O blocks. Do you
have any idea about how to know where are the I/O blocks? Thank you.
Best regards,
  Sitos

2009/12/18 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
> ________________________________
> 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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