http.js

README.adoc

@@ -13048,12 +13048,58 @@ Library support is automatically detected, and only built if you have it install
 
 ===== gem5 only dump selected stats
 
-TODO
-
 https://stackoverflow.com/questions/52014953/how-to-dump-only-a-single-or-certain-selected-stats-in-gem5
 
 To prevent the stats file from becoming humongous.
 
+https://stackoverflow.com/questions/52014953/how-to-dump-only-a-single-or-certain-selected-stats-in-gem5/57221132#57221132
+
+===== Meaning of each gem5 stat
+
+Well, run minimal examples, and reverse engineer them up!
+
+We can start with link:userland/arch/x86_64/freestanding/linux/hello.S[] on atomic with <<gem5-execall-trace-format>>.
+
+....
+./run \
+  --arch aarch64 \
+  --emulator gem5 \
+  --userland userland/arch/aarch64/freestanding/linux/hello.S \
+  --trace ExecAll \
+  --trace-stdout \
+;
+....
+
+which gives:
+
+....
+      0: system.cpu: A0 T0 : @_start    :   movz   x0, #1, #0        : IntAlu :  D=0x0000000000000001  flags=(IsInteger)
+    500: system.cpu: A0 T0 : @_start+4    :   adr   x1, #28            : IntAlu :  D=0x0000000000400098  flags=(IsInteger)
+   1000: system.cpu: A0 T0 : @_start+8    :   ldr   w2, #4194464       : MemRead :  D=0x0000000000000006 A=0x4000a0  flags=(IsInteger|IsMemRef|IsLoad)
+   1500: system.cpu: A0 T0 : @_start+12    :   movz   x8, #64, #0       : IntAlu :  D=0x0000000000000040  flags=(IsInteger)
+   2000: system.cpu: A0 T0 : @_start+16    :   svc   #0x0               : IntAlu :   flags=(IsSerializeAfter|IsNonSpeculative|IsSyscall)
+   2500: system.cpu: A0 T0 : @_start+20    :   movz   x0, #0, #0        : IntAlu :  D=0x0000000000000000  flags=(IsInteger)
+   3000: system.cpu: A0 T0 : @_start+24    :   movz   x8, #93, #0       : IntAlu :  D=0x000000000000005d  flags=(IsInteger)
+   3500: system.cpu: A0 T0 : @_start+28    :   svc   #0x0               : IntAlu :   flags=(IsSerializeAfter|IsNonSpeculative|IsSyscall)
+....
+
+The most important stat of all is usually the cycle count, which is a direct measure of performance if you modelled you system well:
+
+....
+sim_ticks 3500 # Number of ticks simulated
+....
+
+Next, `sim_insts` and `sim_ops` are often critical:
+
+....
+sim_insts 6 # Number of instructions simulated
+sim_ops   6 # Number of ops (including micro ops) simulated
+....
+
+`sim_ops` is like `sim_insts` but it also includes <<gem5-microops>>.
+
+In <<gem5-syscall-emulation-mode>>, syscall instructions are magic, and therefore appear to not be counted, that is why we get 6 instructions instead of 8.
+
 ===== gem5 stats internals
 
 This describes the internals of the <<gem5-m5out-stats-txt-file>>.
@@ -13183,7 +13229,7 @@ On Ubuntu 20.04, you can also see the dot file "directly" with xdot:
 xdot "$(./getvar --arch arm --emulator gem5 m5out_dir)/config.dot"
 ....
 
-which is kind of really cool because it allows you to graph arrows with clicks.
+which is kind of really cool because it allows you to view graph arrows on hover. This can be very useful because the PDF and SVG often overlap so many arrows together that you just can't know which one is coming from/going to where.
 
 It is worth noting that if you are running a bunch of short simulations, dot/SVG/PDF generation could have a significant impact in simulation startup time, so it is something to watch out for. As per https://gem5-review.googlesource.com/c/public/gem5/+/29232 it can be turned off with:
 
@@ -13392,7 +13438,7 @@ A trivial and very direct way to see message would be:
 ....
 ./run \
   --emulator gem5 \
-  --userland \userland/arch/x86_64/freestanding/linux/hello.S \
+  --userland userland/arch/x86_64/freestanding/linux/hello.S \
   --trace-insts-stdout \
   -- \
   --param 'system.cpu[0].max_insts_all_threads = 3' \
@@ -20155,6 +20201,7 @@ MyClassToString { a: 1, b: 2 }
 toString
 my type is MyClassToString and a is 1 and b is 2
 ....
+* link:rootfs_overlay/lkmc/nodejs/http.js[]: `http` module to create a simple HTTP server: https://nodejs.org/api/http.html
 
 ===== NPM