linux-kernel - Re: [patch] preempt: select PREEMPT_DYNAMIC under PREEMPTION instead of PREEMPT

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Date:   Tue, 09 Feb 2021 17:05:14 +0100
From:   Mike Galbraith <efault@....de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch] preempt: select PREEMPT_DYNAMIC under PREEMPTION
 instead of PREEMPT

On Tue, 2021-02-09 at 16:13 +0100, Peter Zijlstra wrote:
> On Tue, Feb 09, 2021 at 02:45:37PM +0100, Mike Galbraith wrote:
> >
> > PREEMPT_RT and PREEMPT both needs PREEMPT_DYNAMIC to build, so move
> > selection of PREEMPT_DYNAMIC to the common denominator, PREEMPTION.
>
> I'm confused, why would you want PREEMPT_DYNAMIC for
> PREEMPT_RT ?
>
> PREEMPT_RT without full preemption is just plain daft, no?

If you turn on PREEMPT, PREEMPT_DYNAMIC is selected because
HAVE_PREEMPT_DYNAMIC is true.

homer:..kernel/linux-tip # grep PREEMPT .config
# CONFIG_PREEMPT_NONE is not set
# CONFIG_PREEMPT_VOLUNTARY is not set
CONFIG_PREEMPT=y
CONFIG_PREEMPT_COUNT=y
CONFIG_PREEMPTION=y
CONFIG_PREEMPT_DYNAMIC=y
CONFIG_PREEMPT_RCU=y
CONFIG_HAVE_PREEMPT_DYNAMIC=y
CONFIG_PREEMPT_NOTIFIERS=y
CONFIG_DRM_I915_PREEMPT_TIMEOUT=640
CONFIG_DEBUG_PREEMPT=y
# CONFIG_PREEMPT_TRACER is not set
# CONFIG_PREEMPTIRQ_DELAY_TEST is not set

Now over to tip-rt, with patchlet...

homer:..kernel/linux-tip-rt # grep PREEMPT .config
CONFIG_HAVE_PREEMPT_LAZY=y
CONFIG_PREEMPT_LAZY=y
# CONFIG_PREEMPT_NONE is not set
# CONFIG_PREEMPT_VOLUNTARY is not set
# CONFIG_PREEMPT is not set
CONFIG_PREEMPT_RT=y
CONFIG_PREEMPT_COUNT=y
CONFIG_PREEMPTION=y
CONFIG_PREEMPT_DYNAMIC=y
CONFIG_PREEMPT_RCU=y
CONFIG_HAVE_PREEMPT_DYNAMIC=y
CONFIG_PREEMPT_NOTIFIERS=y
CONFIG_DRM_I915_PREEMPT_TIMEOUT=640
CONFIG_DEBUG_PREEMPT=y
# CONFIG_PREEMPT_TRACER is not set
# CONFIG_PREEMPTIRQ_DELAY_TEST is not set

...tree builds/runs.  Pop patchlet, and...

  LD      vmlinux.o
  MODPOST vmlinux.symvers
  MODINFO modules.builtin.modinfo
  GEN     modules.builtin
  LD      .tmp_vmlinux.kallsyms1
ld: init/main.o: in function `trace_initcall_start':
/backup/usr/local/src/kernel/linux-tip-rt/./include/trace/events/initcall.h:27: undefined reference to `__SCT__preempt_schedule_notrace'
ld: init/main.o: in function `trace_initcall_finish':
/backup/usr/local/src/kernel/linux-tip-rt/./include/trace/events/initcall.h:48: undefined reference to `__SCT__preempt_schedule_notrace'
ld: init/main.o: in function `trace_initcall_level':
/backup/usr/local/src/kernel/linux-tip-rt/./include/trace/events/initcall.h:10: undefined reference to `__SCT__preempt_schedule_notrace'
ld: init/main.o:(.static_call_sites+0x4): undefined reference to `__SCK__preempt_schedule_notrace'
ld: init/main.o:(.static_call_sites+0x14): undefined reference to `__SCK__preempt_schedule_notrace'
ld: init/main.o:(.static_call_sites+0x24): undefined reference to `__SCK__preempt_schedule_notrace'
ld: arch/x86/entry/vsyscall/vsyscall_64.o: in function `trace_emulate_vsyscall':
/backup/usr/local/src/kernel/linux-tip-rt/arch/x86/entry/vsyscall/vsyscall_trace.h:10: undefined reference to `__SCT__preempt_schedule_notrace'
ld: arch/x86/entry/vsyscall/vsyscall_64.o:(.static_call_sites+0x4): undefined reference to `__SCK__preempt_schedule_notrace'
ld: arch/x86/events/amd/ibs.o: in function `ibs_eilvt_valid':
/backup/usr/local/src/kernel/linux-tip-rt/arch/x86/events/amd/ibs.c:865: undefined reference to `__SCT__preempt_schedule'
ld: arch/x86/events/amd/ibs.o: in function `force_ibs_eilvt_setup':
/backup/usr/local/src/kernel/linux-tip-rt/arch/x86/events/amd/ibs.c:923: undefined reference to `__SCT__preempt_schedule'
ld: /backup/usr/local/src/kernel/linux-tip-rt/arch/x86/events/amd/ibs.c:943: undefined reference to `__SCT__preempt_schedule'
ld: arch/x86/events/amd/ibs.o: in function `ibs_eilvt_valid':
/backup/usr/local/src/kernel/linux-tip-rt/arch/x86/events/amd/ibs.c:865: undefined reference to `__SCT__preempt_schedule'
...