Top-Down Methodology #10
Draft
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
dhschall
pushed a commit
that referenced
this pull request
Jun 10, 2025
…#2346) For a number of common instructions, gem5's built-in ARM disassembler doesn't print the instruction operands. This can be a bit of a headache when you don't want to use libcapstone, and are looking at instruction traces. Reproducer: test.S ``` .text .globl _start _start: ldr x30, [sp] ldr x30, [sp], gem5#16 str x30, [sp] str x30, [sp], gem5#16 ldp x10, x20, [x30] stp x10, x20, [x30] ldp w10, w20, [x30] stp w10, w20, [x30] ldp x10, x20, [x30], #-8 // post-index, negative stp x10, x20, [x30, gem5#16]! // pre-index, write-back ldp w10, w20, [x30, gem5#32] // pre-index, no write-back stp w10, w20, [x30], gem5#128 // post-index, positive dc zva, x17 dc cvac, x17 isb isb #10 dsb nsh dsb sy dsb #8 .long 0xff210110 // m5_op EXIT ``` ``` # Build binary aarch64-linux-gnu-gcc -c test.S -o test.o aarch64-linux-gnu-ld -o test.arm64 test.o -N -Ttext 0x10 -static # objdump disassembly aarch64-linux-gnu-objdump -D test.arm64 # gem5 disassembly ./build/ARM/gem5.opt configs/example/arm/baremetal.py --tarmac-gen --kernel test.arm64 | grep ' IT ' ```
dhschall
requested changes
Jun 16, 2025
There was a problem hiding this comment.
Thanks for already cleaning up things.
The main comment I have at the moment is formatting. Mainly indentation.
Check this: https://github.com/gem5/gem5/pull/2313/files
They will soon merge it. But you might be able to copy already the .clang-format in your gem5 dir and then run git clang-format.
| "Backend Bound, fraction of slots lost due to backend resource " | ||
| "constraints."), | ||
| ADD_STAT( | ||
| retiring, |
| ADD_STAT(fetchLatency, | ||
| statistics::units::Rate<statistics::units::Count, | ||
| statistics::units::Count>::get(), | ||
| "Fetch Latency Bound, frontend stalls due to instruction cache " |
There was a problem hiding this comment.
Its not only instruction cache but also TLB and BTB
src/cpu/o3/cpu.cc
Outdated
| cpu->cpuStats.topDownStats.topDownL1.frontendBound - fetchLatency; | ||
| } | ||
|
|
||
| // CPU::CPUStats::TopDownStats::TopDownFrontendBoundL2::TopDownFrontendBoundL2(CPU |
There was a problem hiding this comment.
Is that not ready or why is it commented?
| statistics::units::Count>::get(), | ||
| "Core Bound, backend stalls due to functional unit constraints") { | ||
| // Backend L2 | ||
| executionStalls = (cpu->iew.instQueue.getStats().numInstsExec0 - |
There was a problem hiding this comment.
This is not properly indented. Should be consistent. 4 spaces.
Same in the lines below and a lot of other places
src/cpu/o3/cpu.cc
Outdated
| statistics::units::Count>::get(), | ||
| "Store Bound") { | ||
| // Backend Bound / Memory Bound L3 | ||
| l1Bound = (cpu->iew.instQueue.getStats().loadStallCycles - |
| @@ -602,9 +615,11 @@ Decode::decode(bool &status_change, ThreadID tid) | |||
| // check if stall conditions have passed | |||
|
|
|||
| if (decodeStatus[tid] == Blocked) { | |||
| ++stats.blockedCycles; | |||
| fetchBubbles -= decodeWidth; | |||
| @@ -299,6 +299,8 @@ class Decode | |||
| */ | |||
| bool squashAfterDelaySlot[MaxThreads]; | |||
|
|
|||
| unsigned fetchBubbles = 0; | |||
There was a problem hiding this comment.
IMHO it's redundant. Just use inst_availabe
| @@ -180,47 +180,58 @@ InstructionQueue::name() const | |||
| InstructionQueue::IQStats::IQStats(CPU *cpu, const unsigned &total_width) | |||
| : statistics::Group(cpu), | |||
| ADD_STAT(instsAdded, statistics::units::Count::get(), | |||
| "Number of instructions added to the IQ (excludes non-spec)"), | |||
| "Number of instructions added to the IQ (excludes non-spec)"), | |||
There was a problem hiding this comment.
Can you revert that. Its not currently indented and not part of your PR
| .flags(statistics::pdf); | ||
| idleRate | ||
| .prereq(idleRate); | ||
| ADD_STAT(predictedBranches, statistics::units::Count::get(), |
There was a problem hiding this comment.
Why did that change? Most of it is still the same.
| ADD_STAT(fetchBubblesMax, statistics::units::Count::get(), | ||
| "Stat for Top-Down Methodology, number of cycles in which no " | ||
| "instructions are delivered to backend") { | ||
| predictedBranches.prereq(predictedBranches); |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
No description provided.