linux-kernel - Re: -tip build failure: trace_clock

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Message-ID: <20090414083239.GD27003@elte.hu>
Date:	Tue, 14 Apr 2009 10:32:39 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: -tip build failure: trace_clock_global undefined

* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> I'm seeing linker errors:
>
>  LD      .tmp_vmlinux1
> arch/x86/kernel/built-in.o: In function `ds_take_timestamp':
> /home/jeremy/git/linux/arch/x86/kernel/ds.c:1380: undefined reference to `trace_clock_global'
> /home/jeremy/git/linux/arch/x86/kernel/ds.c:1380: undefined reference to `trace_clock_global'
> make[2]: *** [.tmp_vmlinux1] Error 1
> make[1]: *** [sub-make] Error 2
> make: *** [all] Error 2
>
>
> .config attached.

Thanks - i pushed out the fix into latest -tip, please re-check it 
works fine for you.

Steve: the reason why randconfig testing had little chance to find 
this was that to trigger the build failure one needs:

 CONFIG_X86_DS=y
 CONFIG_X86_PTRACE_BTS=y
 # CONFIG_FUNCTION_TRACER is not set
 # CONFIG_IRQSOFF_TRACER is not set
 # CONFIG_PREEMPT_TRACER is not set
 # CONFIG_SYSPROF_TRACER is not set
 # CONFIG_SCHED_TRACER is not set
 # CONFIG_CONTEXT_SWITCH_TRACER is not set
 # CONFIG_EVENT_TRACER is not set
 # CONFIG_FTRACE_SYSCALLS is not set
 # CONFIG_BOOT_TRACER is not set
 # CONFIG_TRACE_BRANCH_PROFILING is not set
 # CONFIG_POWER_TRACER is not set
 # CONFIG_STACK_TRACER is not set
 # CONFIG_HW_BRANCH_TRACER is not set
 # CONFIG_KMEMTRACE is not set
 # CONFIG_WORKQUEUE_TRACER is not set
 # CONFIG_BLK_DEV_IO_TRACE is not set
 # CONFIG_MMIOTRACE is not set

It can be seen that this needs 2^17 - in excess of 100,000 
randconfig steps to have a 50% chance of discovery. In the window of 
breakage so far i did 10,000-20,000 randconfig builds so i had no 
realistic chance to see this.

But the real problem is the flatness of the Kconfig space here and 
the loss of a global switch over tracing: IMO we should have a 
global interactive control over CONFIG_TRACING. It's clearly 
something users want and do (like Jeremy did).

We already have a "Tracers" sub-menu under "Kernel Hacking" - it 
should also be dependent on an interactive switch.

( that switch can be default-y so this wont impact visiblity - but
  it will sure improve configurability and testability. )

	Ingo
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