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kernel_module, sample_package: correctly forward Buildroot -O and -g flags

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readme: improve optimization documentation
This commit is contained in:
Ciro Santilli
2018-04-17 14:51:43 +01:00
parent ffa430eef9
commit 50f2518656
5 changed files with 83 additions and 50 deletions
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108
README.adoc
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@@ -54,45 +54,45 @@ which are `printk` messages from `init` and `cleanup` methods of those modules.
Once you use <<gdb>> and <<tmux>>, your terminal will look a bit like this:
....
[ 1.451857] input: AT Translated Set 2 keyboard as /devices/platform/i8042/s1│loading @0xffffffffc0000000: ../kernel_module-1.0//timer.ko
[ 1.454310] ledtrig-cpu: registered to indicate activity on CPUs │(gdb) b lkmc_timer_callback
[ 1.451857] input: AT Translated Set 2 keyboard as /devices/platform/i8042/s1│loading @0xffffffffc0000000: ../kernel_module-1.0//timer.ko
[ 1.454310] ledtrig-cpu: registered to indicate activity on CPUs │(gdb) b lkmc_timer_callback
[ 1.455621] usbcore: registered new interface driver usbhid │Breakpoint 1 at 0xffffffffc0000000: file /home/ciro/bak/git/linux-kernel-module
[ 1.455811] usbhid: USB HID core driver │-cheat/out/x86_64/buildroot/build/kernel_module-1.0/./timer.c, line 28.
[ 1.462044] NET: Registered protocol family 10 │(gdb) c
[ 1.467911] Segment Routing with IPv6 │Continuing.
[ 1.455811] usbhid: USB HID core driver │-cheat/out/x86_64/buildroot/build/kernel_module-1.0/./timer.c, line 28.
[ 1.462044] NET: Registered protocol family 10 │(gdb) c
[ 1.467911] Segment Routing with IPv6 │Continuing.
[ 1.468407] sit: IPv6, IPv4 and MPLS over IPv4 tunneling driver │
[ 1.470859] NET: Registered protocol family 17 │Breakpoint 1, lkmc_timer_callback (data=0xffffffffc0002000 <mytimer>)
[ 1.470859] NET: Registered protocol family 17 │Breakpoint 1, lkmc_timer_callback (data=0xffffffffc0002000 <mytimer>)
[ 1.472017] 9pnet: Installing 9P2000 support │ at /home/ciro/bak/git/linux-kernel-module-cheat/out/x86_64/buildroot/build/
[ 1.475461] sched_clock: Marking stable (1473574872, 0)->(1554017593, -80442)│kernel_module-1.0/./timer.c:28
[ 1.479419] ALSA device list: │28 {
[ 1.479567] No soundcards found. │(gdb) c
[ 1.619187] ata2.00: ATAPI: QEMU DVD-ROM, 2.5+, max UDMA/100 │Continuing.
[ 1.475461] sched_clock: Marking stable (1473574872, 0)->(1554017593, -80442)│kernel_module-1.0/./timer.c:28
[ 1.479419] ALSA device list: │28 {
[ 1.479567] No soundcards found. │(gdb) c
[ 1.619187] ata2.00: ATAPI: QEMU DVD-ROM, 2.5+, max UDMA/100 │Continuing.
[ 1.622954] ata2.00: configured for MWDMA2 │
[ 1.644048] scsi 1:0:0:0: CD-ROM QEMU QEMU DVD-ROM 2.5+ P5│Breakpoint 1, lkmc_timer_callback (data=0xffffffffc0002000 <mytimer>)
[ 1.644048] scsi 1:0:0:0: CD-ROM QEMU QEMU DVD-ROM 2.5+ P5│Breakpoint 1, lkmc_timer_callback (data=0xffffffffc0002000 <mytimer>)
[ 1.741966] tsc: Refined TSC clocksource calibration: 2904.010 MHz │ at /home/ciro/bak/git/linux-kernel-module-cheat/out/x86_64/buildroot/build/
[ 1.742796] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x29dc0f4s│kernel_module-1.0/./timer.c:28
[ 1.743648] clocksource: Switched to clocksource tsc │28 {
[ 2.072945] input: ImExPS/2 Generic Explorer Mouse as /devices/platform/i8043│(gdb) bt
[ 2.078641] EXT4-fs (vda): couldn't mount as ext3 due to feature incompatibis│#0 lkmc_timer_callback (data=0xffffffffc0002000 <mytimer>)
[ 1.742796] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x29dc0f4s│kernel_module-1.0/./timer.c:28
[ 1.743648] clocksource: Switched to clocksource tsc │28 {
[ 2.072945] input: ImExPS/2 Generic Explorer Mouse as /devices/platform/i8043│(gdb) bt
[ 2.078641] EXT4-fs (vda): couldn't mount as ext3 due to feature incompatibis│#0 lkmc_timer_callback (data=0xffffffffc0002000 <mytimer>)
[ 2.080350] EXT4-fs (vda): mounting ext2 file system using the ext4 subsystem│ at /home/ciro/bak/git/linux-kernel-module-cheat/out/x86_64/buildroot/build/
[ 2.088978] EXT4-fs (vda): mounted filesystem without journal. Opts: (null) │kernel_module-1.0/./timer.c:28
[ 2.089872] VFS: Mounted root (ext2 filesystem) readonly on device 254:0. │#1 0xffffffff810ab494 in call_timer_fn (timer=0xffffffffc0002000 <mytimer>,
[ 2.097168] devtmpfs: mounted │ fn=0xffffffffc0000000 <lkmc_timer_callback>) at kernel/time/timer.c:1326
[ 2.126472] Freeing unused kernel memory: 1264K │#2 0xffffffff810ab71f in expire_timers (head=<optimized out>,
[ 2.126706] Write protecting the kernel read-only data: 16384k │ base=<optimized out>) at kernel/time/timer.c:1363
[ 2.129388] Freeing unused kernel memory: 2024K │#3 __run_timers (base=<optimized out>) at kernel/time/timer.c:1666
[ 2.139370] Freeing unused kernel memory: 1284K │#4 run_timer_softirq (h=<optimized out>) at kernel/time/timer.c:1692
[ 2.246231] EXT4-fs (vda): warning: mounting unchecked fs, running e2fsck isd│#5 0xffffffff81a000cc in __do_softirq () at kernel/softirq.c:285
[ 2.259574] EXT4-fs (vda): re-mounted. Opts: block_validity,barrier,user_xatr│#6 0xffffffff810577cc in invoke_softirq () at kernel/softirq.c:365
hello S98 │#7 irq_exit () at kernel/softirq.c:405
│#8 0xffffffff818021ba in exiting_irq () at ./arch/x86/include/asm/apic.h:541
Apr 15 23:59:23 login[49]: root login on 'console' │#9 smp_apic_timer_interrupt (regs=<optimized out>)
hello /root/.profile │ at arch/x86/kernel/apic/apic.c:1052
# insmod /timer.ko │#10 0xffffffff8180190f in apic_timer_interrupt ()
[ 6.791945] timer: loading out-of-tree module taints kernel. │ at arch/x86/entry/entry_64.S:857
# [ 7.821621] 4294894248 │#11 0xffffffff82003df8 in init_thread_union ()
[ 8.851385] 4294894504 │#12 0x0000000000000000 in ?? ()
│(gdb)
[ 2.088978] EXT4-fs (vda): mounted filesystem without journal. Opts: (null) │kernel_module-1.0/./timer.c:28
[ 2.089872] VFS: Mounted root (ext2 filesystem) readonly on device 254:0. │#1 0xffffffff810ab494 in call_timer_fn (timer=0xffffffffc0002000 <mytimer>,
[ 2.097168] devtmpfs: mounted │ fn=0xffffffffc0000000 <lkmc_timer_callback>) at kernel/time/timer.c:1326
[ 2.126472] Freeing unused kernel memory: 1264K │#2 0xffffffff810ab71f in expire_timers (head=<optimized out>,
[ 2.126706] Write protecting the kernel read-only data: 16384k │ base=<optimized out>) at kernel/time/timer.c:1363
[ 2.129388] Freeing unused kernel memory: 2024K │#3 __run_timers (base=<optimized out>) at kernel/time/timer.c:1666
[ 2.139370] Freeing unused kernel memory: 1284K │#4 run_timer_softirq (h=<optimized out>) at kernel/time/timer.c:1692
[ 2.246231] EXT4-fs (vda): warning: mounting unchecked fs, running e2fsck isd│#5 0xffffffff81a000cc in __do_softirq () at kernel/softirq.c:285
[ 2.259574] EXT4-fs (vda): re-mounted. Opts: block_validity,barrier,user_xatr│#6 0xffffffff810577cc in invoke_softirq () at kernel/softirq.c:365
hello S98 │#7 irq_exit () at kernel/softirq.c:405
│#8 0xffffffff818021ba in exiting_irq () at ./arch/x86/include/asm/apic.h:541
Apr 15 23:59:23 login[49]: root login on 'console' │#9 smp_apic_timer_interrupt (regs=<optimized out>)
hello /root/.profile │ at arch/x86/kernel/apic/apic.c:1052
# insmod /timer.ko │#10 0xffffffff8180190f in apic_timer_interrupt ()
[ 6.791945] timer: loading out-of-tree module taints kernel. │ at arch/x86/entry/entry_64.S:857
# [ 7.821621] 4294894248 │#11 0xffffffff82003df8 in init_thread_union ()
[ 8.851385] 4294894504 │#12 0x0000000000000000 in ?? ()
│(gdb)
....
All available modules can be found in the link:kernel_module/[`kernel_module` directory].
@@ -425,6 +425,18 @@ Not all packages have an alias, when they don't, just use the form:
./build -- <pkg>-reconfigure
....
==== Rebuild a package with different build options
For example, if you decide to <<enable-compiler-optimizations>> after an initial build is finished, you must first clean the build before rebuilding:
....
./build -B 'BR2_OPTIMIZE_3=y' kernel_module-dirclean kernel_module-reconfigure
....
as explained at: https://buildroot.org/downloads/manual/manual.html#rebuild-pkg
The clean is necessary because the source files didn't change, so `make` would just check the timestamps and not build anything.
[[retype]]
=== Don't retype arguments all the time
@@ -2447,7 +2459,7 @@ TODO: why does this produce no output?
....
>>> kernel_module 1.0 Building
/usr/bin/make -j8 -C '/home/ciro/bak/git/linux-kernel-module-cheat/out/aarch64/buildroot/build/kernel_module-1.0/user' BR2_PACKAGE_OPENBLAS="" CC="/home/ciro/bak/git/linux-kernel-module-cheat/out/aarch64/buildroot/host/bin/aarch64-buildroot-linux-uclibc-gcc" LD="/home/ciro/bak/git/linux-kernel-module-cheat/out/aarch64/buildroot/host/bin/aarch64-buildroot-linux-uclibc-ld"
/home/ciro/bak/git/linux-kernel-module-cheat/out/aarch64/buildroot/host/bin/aarch64-buildroot-linux-uclibc-gcc -ggdb3 -fopenmp -O0 -std=c99 -Wall -Werror -Wextra -o 'proc_events.out' 'proc_events.c'
/home/ciro/bak/git/linux-kernel-module-cheat/out/aarch64/buildroot/host/bin/aarch64-buildroot-linux-uclibc-gcc -ggdb3 -fopenmp -O0 -std=c99 -Wall -Werror -Wextra -o 'proc_events.out' 'proc_events.c'
In file included from /home/ciro/bak/git/linux-kernel-module-cheat/out/aarch64/buildroot/host/aarch64-buildroot-linux-uclibc/sysroot/usr/include/signal.h:329:0,
from proc_events.c:12:
/home/ciro/bak/git/linux-kernel-module-cheat/out/aarch64/buildroot/host/aarch64-buildroot-linux-uclibc/sysroot/usr/include/sys/ucontext.h:50:16: error: field ‘uc_mcontext’ has incomplete type
@@ -2486,8 +2498,8 @@ msgfmt.c:(.text+0xc2b): undefined reference to `poparser_finish'
collect2: error: ld returned 1 exit status
Makefile.in:120: recipe for target '../utils/msgfmt.host' failed
make[2]: *** [../utils/msgfmt.host] Error 1
package/pkg-generic.mk:227: recipe for target '/data/git/linux-kernel-module-cheat/out/aarch64/buildroot/build/uclibc-custom/.stamp_built' failed
make[1]: *** [/data/git/linux-kernel-module-cheat/out/aarch64/buildroot/build/uclibc-custom/.stamp_built] Error 2
package/pkg-generic.mk:227: recipe for target '/data/git/linux-kernel-module-cheat/out/aarch64/buildroot/build/uclibc-custom/.stamp_built' failed
make[1]: *** [/data/git/linux-kernel-module-cheat/out/aarch64/buildroot/build/uclibc-custom/.stamp_built] Error 2
Makefile:79: recipe for target '_all' failed
make: *** [_all] Error 2
....
@@ -4538,9 +4550,29 @@ You will likely want to change that to:
BR2_OPTIMIZE_3=y
....
and do a full rebuild.
Our link:kernel_module/user[] package correctly forwards the Buildroot options to the build with `$(TARGET_CONFIGURE_OPTS)`, so you don't have to do any extra work.
TODO is it possible to compile a single package with optimizations enabled? In any case, this wouldn't be very representative, since calls to an unoptimized libc will also have an impact on performance. Kernel-wise it should be fine though due to: <<kernel-o0>>
Don't forget to do that if you are <<add-new-buildroot-packages,adding a new package>> with your own build system.
Then, you have two choices:
* if you already have a full `-O0` build, you can choose to rebuild just your package of interest to save some time as described at: <<rebuild-a-package-with-different-build-options>>
+
....
./build -B 'BR2_OPTIMIZE_3=y' kernel_module-dirclean kernel_module-reconfigure
....
+
However, this approach might not be representative since calls to an unoptimized libc and other libraries will have a negative performance impact.
+
Maybe you can get away with rebuilding libc, but I'm not sure that it will work properly.
+
Kernel-wise it should be fine though due to: <<kernel-o0>>
* <<clean-the-build,clean the build>> and rebuild from scratch:
+
....
mv out out~
./build -B 'BR2_OPTIMIZE_3=y'
....
=== Find Buildroot options with make menuconfig