Linux 2.6.37-rc1 Kernel Is Here; Can Build Without BKL

[Tommy666]

Did anybody tried compiling without Big Kernel Lock, this is what I get:

  CHK     include/linux/version.h
  UPD     include/linux/version.h
  CHK     include/generated/utsrelease.h
  UPD     include/generated/utsrelease.h
  HOSTCC  scripts/kallsyms
  CC      scripts/mod/empty.o
  HOSTCC  scripts/mod/mk_elfconfig
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/file2alias.o
  HOSTCC  scripts/mod/modpost.o
  HOSTCC  scripts/mod/sumversion.o
  HOSTCC  scripts/pnmtologo
  HOSTCC  scripts/conmakehash
  HOSTCC  scripts/bin2c
  HOSTLD  scripts/mod/modpost
  CC      kernel/bounds.s
  GEN     include/generated/bounds.h
  CC      arch/x86/kernel/asm-offsets.s
In file included from /usr/src/linux-2.6.37-rc1/arch/x86/include/asm/suspend_64.h:10:0,
                 from /usr/src/linux-2.6.37-rc1/arch/x86/include/asm/suspend.h:4,
                 from arch/x86/kernel/asm-offsets_64.c:20,
                 from arch/x86/kernel/asm-offsets.c:4:
/usr/src/linux-2.6.37-rc1/arch/x86/include/asm/i387.h: In function ?irq_ts_save?:
/usr/src/linux-2.6.37-rc1/arch/x86/include/asm/i387.h:324:2: error: implicit declaration of function ?kernel_locked?
make[1]: *** [arch/x86/kernel/asm-offsets.s] Error 1
make: *** [prepare0] Error 2
[root@phenon linux-2.6.37-rc1]# make
  CHK     include/linux/version.h
  CHK     include/generated/utsrelease.h
  CC      arch/x86/kernel/asm-offsets.s
In file included from /usr/src/linux-2.6.37-rc1/arch/x86/include/asm/suspend_64.h:10:0,
                 from /usr/src/linux-2.6.37-rc1/arch/x86/include/asm/suspend.h:4,
                 from arch/x86/kernel/asm-offsets_64.c:20,
                 from arch/x86/kernel/asm-offsets.c:4:
/usr/src/linux-2.6.37-rc1/arch/x86/include/asm/i387.h: In function ?irq_ts_save?:
/usr/src/linux-2.6.37-rc1/arch/x86/include/asm/i387.h:324:2: error: implicit declaration of function ?kernel_locked?
make[1]: *** [arch/x86/kernel/asm-offsets.s] Error 1
make: *** [prepare0] Error 2
[root@phenon linux-2.6.37-rc1]#

I get the same error....

[smitty3268]

iam not native english, i already reed giant lock, but dont understand anything [nothing seems to be more clear]

both, benchmarks and explanations

A lock is a synchronization primitive. Basically you place it around blocks of code, and then it becomes impossible for 1 thread to enter the block until the first has exited. The idea is to keep 1 thread from deleting or modifying some shared data before another thread has finished using it. In a userspace program that is only an issue for multi-threaded applications. In the kernel, there are all sorts of threads, events, and hardware interrupts that can cause an issue.

A long time ago, devs originally create 1 large lock and used it everywhere in the kernel. That was simple to do, because essentially grabbing the lock switched all the code inside into a single-threaded mode. But it has issues with scalability - you want as many different threads as possible able to work. There's no reason the memory subsystem and the Ext4 filesystem should both be blocking each other. So the solution is to create 2 locks, one for each section. The complication is that so much complicated code had come to rely on the single lock that it was almost impossible to predict the behavior of the kernel when you messed with that global lock. So people have been slowly going through section by section of the kernel to try and factor out what codes needs to share the same lock and what code can be separated out. A lot of the code under the global lock didn't even need to be, and was just there because the original coder thought it might be an issue.

So I'm not really sure how benchmarks will change. It will definitely increase the scalability of anything that likes to hit a bunch of kernel code. But on the other hand, this has been going on piece by piece for many years. So a lot of the benefits were already done and in previous kernels.

[hax0r]

Did anybody tried compiling without Big Kernel Lock, this is what I get:

  CHK     include/linux/version.h
  UPD     include/linux/version.h
  CHK     include/generated/utsrelease.h
  UPD     include/generated/utsrelease.h
  HOSTCC  scripts/kallsyms
  CC      scripts/mod/empty.o
  HOSTCC  scripts/mod/mk_elfconfig
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/file2alias.o
  HOSTCC  scripts/mod/modpost.o
  HOSTCC  scripts/mod/sumversion.o
  HOSTCC  scripts/pnmtologo
  HOSTCC  scripts/conmakehash
  HOSTCC  scripts/bin2c
  HOSTLD  scripts/mod/modpost
  CC      kernel/bounds.s
  GEN     include/generated/bounds.h
  CC      arch/x86/kernel/asm-offsets.s
In file included from /usr/src/linux-2.6.37-rc1/arch/x86/include/asm/suspend_64.h:10:0,
                 from /usr/src/linux-2.6.37-rc1/arch/x86/include/asm/suspend.h:4,
                 from arch/x86/kernel/asm-offsets_64.c:20,
                 from arch/x86/kernel/asm-offsets.c:4:
/usr/src/linux-2.6.37-rc1/arch/x86/include/asm/i387.h: In function ?irq_ts_save?:
/usr/src/linux-2.6.37-rc1/arch/x86/include/asm/i387.h:324:2: error: implicit declaration of function ?kernel_locked?
make[1]: *** [arch/x86/kernel/asm-offsets.s] Error 1
make: *** [prepare0] Error 2
[root@phenon linux-2.6.37-rc1]# make
  CHK     include/linux/version.h
  CHK     include/generated/utsrelease.h
  CC      arch/x86/kernel/asm-offsets.s
In file included from /usr/src/linux-2.6.37-rc1/arch/x86/include/asm/suspend_64.h:10:0,
                 from /usr/src/linux-2.6.37-rc1/arch/x86/include/asm/suspend.h:4,
                 from arch/x86/kernel/asm-offsets_64.c:20,
                 from arch/x86/kernel/asm-offsets.c:4:
/usr/src/linux-2.6.37-rc1/arch/x86/include/asm/i387.h: In function ?irq_ts_save?:
/usr/src/linux-2.6.37-rc1/arch/x86/include/asm/i387.h:324:2: error: implicit declaration of function ?kernel_locked?
make[1]: *** [arch/x86/kernel/asm-offsets.s] Error 1
make: *** [prepare0] Error 2
[root@phenon linux-2.6.37-rc1]#

[NomadDemon]

iam not native english, i already reed giant lock, but dont understand anything [nothing seems to be more clear]

both, benchmarks and explanations

[droidhacker]

whats the difference between BKL and nonBKL ?
any charts? tests? something?

Are you asking for an explanation or benchmarks?

If you want an explanation, wikipedia under "giant lock" has an explanation that might help you understand it better.

[NomadDemon]

whats the difference between BKL and nonBKL ?
any charts? tests? something?

[smitty3268]

I don't know if it will result in performance improvement, but I believe that this was not the major motivation. The major motivation is that it was one big scary voodoo which nobody really understood anymore.

There were certain places where i think it limited performance, but whether that will be noticeable by a desktop user I'm not sure. I think it was important for things like RT linux as well. The real gain is that now driver and subsystem maintainers can work in their code without having to worry about messing up the BKL in weird ways for everyone else that is using it across the whole kernel.

[nkef]

Is there any progress with Linux responsiveness problems
as reported in:

https://bugzilla.kernel.org/show_bug.cgi?id=12309

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/131094

[pingufunkybeat]

I think the problem is that V4L manually locks and unlocks the BKL, which will not work if BKL is not used. It will have to be ported, like most core subsystems have been already.

I don't know if it will result in performance improvement, but I believe that this was not the major motivation. The major motivation is that it was one big scary voodoo which nobody really understood anymore.

[korpenkraxar]

Will a kernel w/o Big Kernel Lock itself result in any noticeable performance difference for a Desktop user?

What kind of functionality is currently tied to V4L? Webcams?

How does BKL apply to V4L2?