24.22.4.8.5. gem5 event queue DerivO3CPU syscall emulation freestanding example analysis: stall_gain
Like gem5 event queue DerivO3CPU syscall emulation freestanding example analysis: stall but now with an LDR stall: userland/arch/aarch64/freestanding/linux/stall_gain.S.
So in this case we see that there were actual potential gains, since the movz x11 started running immediately. We just stopped at movz x20 because a new ifetch was needed.
// f = fetch, d = decode, n = rename, p = dispatch, i = issue, c = complete, r = retire
timeline tick pc.upc disasm seq_num
[.ic.r........................................................................fdn]-( 40000) 0x004000b0.0 movz x0, #0, #0 [ 1]
[.ic.r........................................................................fdn]-( 40000) 0x004000b4.0 movz x1, #1, #0 [ 2]
[.ic.r........................................................................fdn]-( 40000) 0x004000b8.0 movz x2, #4, #0 [ 3]
[.ic.r........................................................................fdn]-( 40000) 0x004000bc.0 movz x3, #5, #0 [ 4]
[....................fdn.ic.r....................................................]-( 120000) 0x004000c0.0 adr x4, #65772 [ 5]
[....................fdn.pic.....................................................]-( 120000) 0x004000c4.0 ldr x5, [x4] [ 6]
[........................................................r.......................]-( 160000) ...
[....................fdn.ic......................................................]-( 120000) 0x004000c8.0 movz x6, #6, #0 [ 7]
[........................................................r.......................]-( 160000) ...
[....................fdn.ic......................................................]-( 120000) 0x004000cc.0 movz x7, #7, #0 [ 8]
[........................................................r.......................]-( 160000) ...
[....................fdn.ic......................................................]-( 120000) 0x004000d0.0 movz x8, #8, #0 [ 9]
[........................................................r.......................]-( 160000) ...
[....................fdn.ic......................................................]-( 120000) 0x004000d4.0 movz x9, #9, #0 [ 10]
[........................................................r.......................]-( 160000) ...
[....................fdn.ic......................................................]-( 120000) 0x004000d8.0 movz x10, #10, #0 [ 11]
[........................................................r.......................]-( 160000) ...
[....................fdn.pic.....................................................]-( 120000) 0x004000dc.0 movz x11, #11, #0 [ 12]
[........................................................r.......................]-( 160000) ...
[.....................fdn.ic.....................................................]-( 120000) 0x004000e0.0 movz x12, #12, #0 [ 13]
[........................................................r.......................]-( 160000) ...
[.....................fdn.ic.....................................................]-( 120000) 0x004000e4.0 movz x13, #13, #0 [ 14]
[.........................................................r......................]-( 160000) ...
[.....................fdn.ic.....................................................]-( 120000) 0x004000e8.0 movz x14, #14, #0 [ 15]
[.........................................................r......................]-( 160000) ...
[.....................fdn.ic.....................................................]-( 120000) 0x004000ec.0 movz x15, #15, #0 [ 16]
[.........................................................r......................]-( 160000) ...
[.....................fdn.ic.....................................................]-( 120000) 0x004000f0.0 movz x16, #16, #0 [ 17]
[.........................................................r......................]-( 160000) ...
[.....................fdn.pic....................................................]-( 120000) 0x004000f4.0 movz x17, #17, #0 [ 18]
[.........................................................r......................]-( 160000) ...
[.....................fdn.pic....................................................]-( 120000) 0x004000f8.0 movz x18, #18, #0 [ 19]
[.........................................................r......................]-( 160000) ...
[.....................fdn.pic....................................................]-( 120000) 0x004000fc.0 movz x19, #19, #0 [ 20]
[.........................................................r......................]-( 160000) ...
[............................................fdn.ic.......r......................]-( 160000) 0x00400100.0 movz x20, #20, #0 [ 21]
[............................................fdn.ic........r.....................]-( 160000) 0x00400104.0 movz x21, #21, #0 [ 22]
[............................................fdn.ic........r.....................]-( 160000) 0x00400108.0 movz x22, #22, #0 [ 23]
[............................................fdn.ic........r.....................]-( 160000) 0x0040010c.0 movz x23, #23, #0 [ 24]
[............................................fdn.ic........r.....................]-( 160000) 0x00400110.0 movz x24, #24, #0 [ 25]
[............................................fdn.ic........r.....................]-( 160000) 0x00400114.0 movz x25, #25, #0 [ 26]
[............................................fdn.pic.......r.....................]-( 160000) 0x00400118.0 movz x26, #26, #0 [ 27]
[............................................fdn.pic.......r.....................]-( 160000) 0x0040011c.0 movz x27, #27, #0 [ 28]
[.............................................fdn.ic.......r.....................]-( 160000) 0x00400120.0 movz x28, #28, #0 [ 29]
[.............................................fdn.ic........r....................]-( 160000) 0x00400124.0 movz x29, #29, #0 [ 30]
[.............................................fdn.ic........r....................]-( 160000) 0x00400128.0 movz x0, #0, #0 [ 31]
[.............................................fdn.ic........r....................]-( 160000) 0x0040012c.0 movz x1, #1, #0 [ 32]
[.............................................fdn.pic.......r....................]-( 160000) 0x00400130.0 movz x2, #2, #0 [ 33]
[.............................................fdn.pic.......r....................]-( 160000) 0x00400134.0 movz x3, #3, #0 [ 34]
[.............................................fdn.pic.......r....................]-( 160000) 0x00400138.0 movz x4, #4, #0 [ 35]
[.............................................fdn.pic.......r....................]-( 160000) 0x0040013c.0 movz x5, #5, #0 [ 36]
We now also understand the graph better from lines such as this:
[....................fdn.pic.....................................................]-( 120000) 0x004000c4.0 ldr x5, [x4] [ 6] [........................................................r.......................]-( 160000) ... [....................fdn.ic......................................................]-( 120000) 0x004000c8.0 movz x6, #6, #0 [ 7] [........................................................r.......................]-( 160000) ...
We see that extra lines are drawn (the 160000 … lines here) whenever something stalls for a period longer than the width of the visualisation.
Things are still relatively readable because the wrapping aligns them with events that actually happened on that line directly e.g. 160000) 0x00400100.0 movz x20, #20, #0..
But from this we kind of see the need for: gem5 Konata O3 pipeline viewer.