Hi Prof. Jason, Thank you for the clarification. I further wanted to ask whether there is any other way to do multithreaded application tests correctly in SE+ruby mode? If not, then we'll be forced to use FS mode which afaik does not work currently with MSI (our modified protocol will have to be changed again because FS mode requires (?) DMA support). Do you have any advice for things to watch out for while testing our multithreaded applications in Full System mode?
Thanks and Regards, Gautam Pathak ________________________________ From: Jason Lowe-Power <ja...@lowepower.com> Sent: Friday, September 2, 2022 10:51 AM To: The gem5 Users mailing list <gem5-users@gem5.org> Subject: [gem5-users] Re: Trying to add barrier to threads example Hi Gautam, Functional accesses (i.e., fake/debug accesses that bypass all timing) and Ruby do not play well together. Fundamentally, it is hard to know what is the most up to date value or which value(s) you have to update when a cache block is in an intermediate state. With MI_example and MESI, these protocols probably have more support for functional reads than MSI, but you're also just getting lucky with those. At some point, if you're doing functional accesses, it's going to fail. In SE mode, to implement the fake system calls which execute *in the simulator* instead of via the guest kernel executing on the simulated CPU, we must use the fake/unrealistic/magic functional accesses. So, this is why SE mode + multithreading + Ruby will almost always run into a problem at some point. FS mode will not have this issue because it does not use functional accesses (almost none at all) and nothing is "faked." The simulated CPU executes all of the kernel system calls. Hopefully this answers your question. Let me know if I can provide more info :) Cheers, Jason On Thu, Sep 1, 2022 at 3:58 PM Gautam Pathak <gautam.pat...@uwaterloo.ca<mailto:gautam.pat...@uwaterloo.ca>> wrote: Hi All, I'm trying to add a custom thread barrier to the array_add function by using __sync_fetch_and_add. The system I'm using is MSI using Ruby in SE mode. When I run this, I get the following error: build/X86/mem/ruby/system/RubyPort.cc:434: fatal: Ruby functional read failed for address 0x15b918. Till now I have observed that there is an open issue which mentions that Ruby+multithreading+SE is not supported. The exact fault occurs in Futex syscall. (Ref. https://gem5.atlassian.net/browse/GEM5-676). However, I have tested the same for MI_Example protocol (using simple_ruby.py) and MESI_Two_Level (using se.py) upto 30+ threads and it works. This makes me wonder whether this is an MSI protocol bug. Any suggestions on how I should go on about this issue would be appreciated! Otherwise, is Full System mode the recommended option for Ruby+custom coherence protocol+multithreading (possibly using atomics)? Thanks and Regards, Gautam Pathak _______________________________________________ gem5-users mailing list -- gem5-users@gem5.org<mailto:gem5-users@gem5.org> To unsubscribe send an email to gem5-users-le...@gem5.org<mailto:gem5-users-le...@gem5.org>
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