Hi Malek,
I find this statement puzzling: "before the functional access completes". A
functional access is purely a chain of function calls that complete in 0 time.
How can anything happen before it completes?
Thanks,
Andreas
From: Malek Musleh <[email protected]<mailto:[email protected]>>
Reply-To: gem5 users mailing list
<[email protected]<mailto:[email protected]>>
Date: Thursday, 1 August 2013 16:38
To: gem5 users mailing list <[email protected]<mailto:[email protected]>>
Subject: [gem5-users] Functional Accesses Failing in Ruby
Hi,
I am running into a problem with one of my simulations where a functional read
accss is failing. It is failing in this case because as the RubySystem is
handling the functional accesses, it checks all the controllers in the system
to determine which controllers have the block with the necesary permissions
(RW/RO) and which have unavailable (I/BUSY).
For this specific case, the block is only valid in one cache, and is at the tme
in 'M' state which has RW permission. Then, a L1_Replacement event is triggered
in between the LOAD on M, and before the functional access completes, such that
when the ruby system checks, it only finds one copy of the block, that copy
being in MI (BUSY) state as it is being written back.
Searching the list, it looks like this is a general (although rare) problem
that can occur due to functional accesses coexisting with timing accesses:
http://www.mail-archive.com/[email protected]/msg02126.html
In solving that problem, the access permission of the WB state was changed to
allow read permissions, but I am hesitant about doing that for the MI state in
the MOESI_CMP_directory protocol, as it might have other negative effects.
I am not using the latest latest dev repo (about a couple of months old), and I
have made changes to the code, not any of which affects this behavior, it just
exposed the problem.
I have noticed a few others on the list have experienced similar problems, but
no solution/response was ever posted.
Any body have a better/cleaner idea than to change the access permissions of
the MI State?
Below is a snippet of the protocol trace/RubySystem flag:
2499502566500 0 L1Cache Load M>M [0x7510000,
line 0x7510000]
2499527076000 0 L1Cache L1_Replacement M>MI [0x7510000,
line 0x7510000]
2499527078000 0 L2Cache L1_PUTX ILX>ILXW [0x7510000,
line 0x7510000]
2499527082000 0 L1Cache Writeback_Ack_Data MI>I [0x7510000,
line 0x7510000]
2499527084000 0 L2Cache L1_WBDIRTYDATA ILXW>M [0x7510000,
line 0x7510000]
2499530130500 0 Seq Begin > [0x7510000,
line 0x7510000] LD
2499530132000 0 L1Cache Load I>IS [0x7510000,
line 0x7510000]
2499530134000 0 L2Cache L1_GETS M>OO [0x7510000,
line 0x7510000]
2499530136000 0 Seq Done > [0x7510000,
line 0x7510000] 11 cycles
2499530136000 0 L1Cache Exclusive_Data IS>M_W [0x7510000,
line 0x7510000]
2499530138000 0 L2Cache Exclusive_Unblock OO>ILX [0x7510000,
line 0x7510000]
2499530161000 0 L1Cache Use_Timeout M_W>M [0x7510000,
line 0x7510000]
2499531935500 0 Seq Begin > [0x7510000,
line 0x7510000] LD
2499531937000 0 Seq Done > [0x7510000,
line 0x7510000] 3 cycles
2499531937000 0 L1Cache Load M>M [0x7510000,
line 0x7510000]
2499663708000: system.ruby: Functional Read request for [0x7510000, line
0x7510000]
2499663888000: system.ruby: Functional Read request for [0x7510000, line
0x7510000]
2499664653000 0 L1Cache L1_Replacement M>MI [0x7510000,
line 0x7510000]
2499664661500: system.ruby: Functional Read request for [0x7510000, line
0x7510000]
fatal: Ruby functional read failed for address 0x7510000
Malek
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