3rd-party/linux-kernel-module-cheat
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Backend simple

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Ciro Santilli
2017-09-29 23:35:02 +01:00
parent 401c747eee
commit 467923860b
2 changed files with 15 additions and 5 deletions
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18
README.md
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@@ -567,6 +567,7 @@ says:
- <https://www.quora.com/How-many-instructions-does-a-typical-Linux-kernel-boot-take> - <https://www.quora.com/How-many-instructions-does-a-typical-Linux-kernel-boot-take>
- <https://github.com/cirosantilli/chat/issues/31> - <https://github.com/cirosantilli/chat/issues/31>
- <https://rwmj.wordpress.com/2016/03/17/tracing-qemu-guest-execution/> - <https://rwmj.wordpress.com/2016/03/17/tracing-qemu-guest-execution/>
- `qemu/docs/tracing.txt` and `qemu/docs/replay.txt`
Naive attempt: add to `S99`: Naive attempt: add to `S99`:
@@ -575,9 +576,18 @@ Naive attempt: add to `S99`:
Then run as: Then run as:
time ./runqemu -n -- -trace exec_tb,file=trace time ./runqemu -n -- -trace exec_tb,file=trace
./qemu/scripts/simpletrace.py qemu/trace-events trace >trace.txt
wc -l trace wc -l trace
This requires the simple QEMU patch mentioned at: <https://rwmj.wordpress.com/2016/03/17/tracing-qemu-guest-execution/> This requires:
- `./configure --enable-trace-backends=simple`. This logs in a binary format to the trace file.
It makes 3x execution faster than the default trace backend which logs human readable data to stdout.
This also alters the actual execution, and reduces the instruction count by 10M TODO understand exactly why, possibly due to the `All QSes seen` thing.
- the simple QEMU patch mentioned at: <https://rwmj.wordpress.com/2016/03/17/tracing-qemu-guest-execution/>
Possible improvements: Possible improvements:
@@ -585,7 +595,7 @@ Possible improvements:
- disable networking. Is replacing `init` enough? - disable networking. Is replacing `init` enough?
- logging greatly slows down the CPU, and leads to this: - logging with the default backend `log` greatly slows down the CPU, and in particular leads to this during kernel boot:
All QSes seen, last rcu_sched kthread activity 5252 (4294901421-4294896169), jiffies_till_next_fqs=1, root ->qsmask 0x0 All QSes seen, last rcu_sched kthread activity 5252 (4294901421-4294896169), jiffies_till_next_fqs=1, root ->qsmask 0x0
swapper/0 R running task 0 1 0 0x00000008 swapper/0 R running task 0 1 0 0x00000008
@@ -597,9 +607,9 @@ Possible improvements:
[<ffffffff810a41d1>] rcu_check_callbacks+0x871/0x880 [<ffffffff810a41d1>] rcu_check_callbacks+0x871/0x880
[<ffffffff810a799f>] update_process_times+0x2f/0x60 [<ffffffff810a799f>] update_process_times+0x2f/0x60
Is it harmless, or does it change timings considerably. in which the boot appears to hang for a considerable time.
- Confirm that the kernel enters at `0x1000000`. - Confirm that the kernel enters at `0x1000000`, or where it enters. Once we have this, we can exclude what comes before in the BIOS.
## Table of contents ## Table of contents

2
run
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@@ -51,7 +51,7 @@ env \
make \ make \
O="$outdir" \ O="$outdir" \
BR2_JLEVEL="$(($(nproc) - 2))" \ BR2_JLEVEL="$(($(nproc) - 2))" \
HOST_QEMU_OPTS="--enable-debug --enable-sdl --extra-cflags='-DDEBUG_PL061=1' --with-sdlabi=2.0" \ HOST_QEMU_OPTS="--enable-debug --enable-sdl --extra-cflags='-DDEBUG_PL061=1' --with-sdlabi=2.0 --enable-trace-backends=simple" \
kernel_module-rebuild \ kernel_module-rebuild \
$extra_targets \ $extra_targets \
all \ all \