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From: Steven Rostedt <rostedt@goodmis.org>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Christoph Hellwig <hch@infradead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
	Gregory Haskins <ghaskins@novell.com>,
	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tim Bird <tim.bird@am.sony.com>, Sam Ravnborg <sam@ravnborg.org>,
	"Frank Ch. Eigler" <fche@redhat.com>,
	Steven Rostedt <srostedt@redhat.com>,
	Philippe Gerum <rpm@xenomai.org>
Subject: Re: [RFC PATCH 01/22 -v2] Add basic support for gcc profiler instrumentation
Date: Thu, 10 Jan 2008 14:54:04 -0500 (EST)	[thread overview]
Message-ID: <Pine.LNX.4.58.0801101411000.15391@gandalf.stny.rr.com> (raw)
In-Reply-To: <478661B9.7050406@siemens.com>


On Thu, 10 Jan 2008, Jan Kiszka wrote:

> Steven Rostedt wrote:
> > Index: linux-compile-i386.git/Makefile
> > ===================================================================
> > --- linux-compile-i386.git.orig/Makefile	2008-01-09 14:09:36.000000000 -0500
> > +++ linux-compile-i386.git/Makefile	2008-01-09 14:10:07.000000000 -0500
> > @@ -509,6 +509,10 @@ endif
> >
> >  include $(srctree)/arch/$(SRCARCH)/Makefile
> >
> > +# MCOUNT expects frame pointer
>
> This comment looks stray.

Actually it's not ;-)

The original code had something like this:

#if CONFIG_MCOUNT
KBUILD_CFLAGS += ...
#else
#if CONFIG_FRAME_POINTER
KBUILD_CFLAGS += ...
#else
KBUILD_CFLAGS += ...
#endif
#endif

And Sam Ravnborg suggested to put that logic into the Kbuild system. For
which I did, but I put that comment there to just let others know that
MCOUNT expects the flags of FRAME_POINTER. But, I guess we can nuke that
comment anyway. It just leads to confusion.

>
> > +ifdef CONFIG_MCOUNT
> > +KBUILD_CFLAGS	+= -pg
> > +endif
> >  ifdef CONFIG_FRAME_POINTER
> >  KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
> >  else
> > Index: linux-compile-i386.git/arch/x86/Kconfig
> > ===================================================================
> > --- linux-compile-i386.git.orig/arch/x86/Kconfig	2008-01-09 14:09:36.000000000 -0500
> > +++ linux-compile-i386.git/arch/x86/Kconfig	2008-01-09 14:10:07.000000000 -0500
> > @@ -28,6 +28,10 @@ config GENERIC_CMOS_UPDATE
> >  	bool
> >  	default y
> >
> > +config ARCH_HAS_MCOUNT
> > +       bool
> > +       default y
> > +
> >  config CLOCKSOURCE_WATCHDOG
> >  	bool
> >  	default y
> > Index: linux-compile-i386.git/arch/x86/kernel/Makefile_32
> > ===================================================================
> > --- linux-compile-i386.git.orig/arch/x86/kernel/Makefile_32	2008-01-09 14:09:36.000000000 -0500
> > +++ linux-compile-i386.git/arch/x86/kernel/Makefile_32	2008-01-09 14:10:07.000000000 -0500
> > @@ -23,6 +23,7 @@ obj-$(CONFIG_APM)		+= apm_32.o
> >  obj-$(CONFIG_X86_SMP)		+= smp_32.o smpboot_32.o tsc_sync.o
> >  obj-$(CONFIG_SMP)		+= smpcommon_32.o
> >  obj-$(CONFIG_X86_TRAMPOLINE)	+= trampoline_32.o
> > +obj-$(CONFIG_MCOUNT)		+= mcount-wrapper.o
>
> So far the code organization is different for 32 and 64 bit. I would
> suggest to either
>
>  o move both trampolines into entry_*.S or
>  o put them in something like mcount-wrapper_32/64.S.

Yeah, that's a relic from -rt. I never liked that, but I was just too lazy
to change it. I think I'll move the mcount_wrapper into entry_32.S

>
> >  obj-$(CONFIG_X86_MPPARSE)	+= mpparse_32.o
> >  obj-$(CONFIG_X86_LOCAL_APIC)	+= apic_32.o nmi_32.o
> >  obj-$(CONFIG_X86_IO_APIC)	+= io_apic_32.o
> > Index: linux-compile-i386.git/arch/x86/kernel/mcount-wrapper.S
> > ===================================================================
> > --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> > +++ linux-compile-i386.git/arch/x86/kernel/mcount-wrapper.S	2008-01-09 14:10:07.000000000 -0500
> > @@ -0,0 +1,25 @@
> > +/*
> > + *  linux/arch/x86/mcount-wrapper.S
> > + *
> > + *  Copyright (C) 2004 Ingo Molnar
> > + */
> > +
> > +.globl mcount
> > +mcount:
> > +	cmpl $0, mcount_enabled
> > +	jz out
> > +
> > +	push %ebp
> > +	mov %esp, %ebp
>
> What is the benefit of having a call frame in this trampoline? We used
> to carry this in the i386 mcount tracer for Adeos/I-pipe too (it was
> derived from the -rt code), but I just successfully tested a removal
> patch. Also glibc [1] doesn't include it.

Hmm, what about having frame pointers on? Isn't that a requirement?

>
> > +	pushl %eax
> > +	pushl %ecx
> > +	pushl %edx
> > +
> > +	call __mcount
>
> I think this indirection should be avoided, just like the 64-bit version
> and glibc do.

I thought about that too, but didn't have the time to look into the
calling convention for that. <does a quick look at glibc>

# objdump --start-address 0x`nm /lib/libc-2.7.so | sed -ne '/ mcount$/s/^\([0-9a-f]*\).*/\1/p'` -D /lib/libc-2.7.so |head -28 |tail -12
49201cd0 <_mcount>:
49201cd0:       50                      push   %eax
49201cd1:       51                      push   %ecx
49201cd2:       52                      push   %edx
49201cd3:       8b 54 24 0c             mov    0xc(%esp),%edx
49201cd7:       8b 45 04                mov    0x4(%ebp),%eax
49201cda:       e8 91 f4 ff ff          call   49201170
<__mcount_internal>
49201cdf:       5a                      pop    %edx
49201ce0:       59                      pop    %ecx
49201ce1:       58                      pop    %eax
49201ce2:       c3                      ret
49201ce3:       90                      nop

Until I found out about the frame pointers, I'll leave in the ebp copy.

>
> > +
> > +	popl %edx
> > +	popl %ecx
> > +	popl %eax
> > +	popl %ebp
> > +out:
> > +	ret
>
> ....

[...]

> > +/** __mcount - hook for profiling
> > + *
> > + * This routine is called from the arch specific mcount routine, that in turn is
> > + * called from code inserted by gcc -pg.
> > + */
> > +notrace void __mcount(void)
> > +{
> > +	mcount_trace_function(CALLER_ADDR1, CALLER_ADDR2);
> > +}
>
> mcount_trace_function should always be called from the assembly
> trampoline, IMO.

I'll try that.

> > Index: linux-compile-i386.git/include/linux/mcount.h
> > ===================================================================
> > --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> > +++ linux-compile-i386.git/include/linux/mcount.h	2008-01-09 15:17:20.000000000 -0500
> > @@ -0,0 +1,21 @@
> > +#ifndef _LINUX_MCOUNT_H
> > +#define _LINUX_MCOUNT_H
> > +
> > +#ifdef CONFIG_MCOUNT
> > +extern int mcount_enabled;
> > +
> > +#include <linux/linkage.h>
> > +
> > +#define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
> > +#define CALLER_ADDR1 ((unsigned long)__builtin_return_address(1))
> > +#define CALLER_ADDR2 ((unsigned long)__builtin_return_address(2))
>
> Still used when __mcount would be gone?

Will be used later on by the tracers. Actually, I wish this was in a more
generic kernel header, since I find myself typing
"__builtin_return_address" quite often.

>
> > +
> > +typedef void (*mcount_func_t)(unsigned long ip, unsigned long parent_ip);
> > +
> > +extern void mcount(void);
> > +
> > +int register_mcount_function(mcount_func_t func);
> > +void clear_mcount_function(void);
> > +
> > +#endif /* CONFIG_MCOUNT */
> > +#endif /* _LINUX_MCOUNT_H */
> > Index: linux-compile-i386.git/arch/x86/kernel/entry_64.S
> > ===================================================================
> > --- linux-compile-i386.git.orig/arch/x86/kernel/entry_64.S	2008-01-09 14:09:36.000000000 -0500
> > +++ linux-compile-i386.git/arch/x86/kernel/entry_64.S	2008-01-09 14:10:07.000000000 -0500
> > @@ -53,6 +53,46 @@
> >
> >  	.code64
> >
> > +#ifdef CONFIG_MCOUNT
> > +
> > +ENTRY(mcount)
> > +	cmpl $0, mcount_enabled
> > +	jz out
> > +
> > +	push %rbp
> > +	mov %rsp,%rbp
>
> Same as for x86_32.

Same checking for frame pointers too.

>
> > +
> > +	push %r11
> > +	push %r10
>
> glibc [2] doesn't save those two, and we were also happy without them so
> far. Or are there nasty corner-cases in the kernel?

Probably not. I'll see what happens without them.

>
> > +	push %r9
> > +	push %r8
> > +	push %rdi
> > +	push %rsi
> > +	push %rdx
> > +	push %rcx
> > +	push %rax
>
> SAVE_ARGS/RESTORE_ARGS and glibc use explicit rsp manipulation + movq
> instead of push/pop. I wonder if there is a small advantage, but I'm not
> that deep into this arch.

Yeah, it's probably a bit faster to do the mov instead. I'll add that.

>
> > +
> > +	mov 0x0(%rbp),%rax
> > +	mov 0x8(%rbp),%rdi
> > +	mov 0x8(%rax),%rsi
>
> See [2] for saving one instruction here. :)

hehe, yeah, will do.

>
> > +
> > +	call   *mcount_trace_function
> > +
> > +	pop %rax
> > +	pop %rcx
> > +	pop %rdx
> > +	pop %rsi
> > +	pop %rdi
> > +	pop %r8
> > +	pop %r9
> > +	pop %r10
> > +	pop %r11
> > +
> > +	pop %rbp
> > +out:
> > +	ret
> > +#endif
> > +
> >  #ifndef CONFIG_PREEMPT
> >  #define retint_kernel retint_restore_args
> >  #endif
>
> This generic approach is very appreciated here as well. It would take
> away the burden of maintaining the arch-dependent stubs within I-pipe.
>
> What we could contribute later on is a blackfin trampoline, there is
> just still a bug in their toolchain which breaks mcount for modules. But
> I could check with the bfin guys again about the progress and underline
> the importance of this long-pending issue.

Thanks,

-- Steve


  reply	other threads:[~2008-01-10 19:55 UTC|newest]

Thread overview: 100+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-09 23:29 [RFC PATCH 00/22 -v2] mcount and latency tracing utility -v2 Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 01/22 -v2] Add basic support for gcc profiler instrumentation Steven Rostedt
2008-01-10 18:19   ` Jan Kiszka
2008-01-10 19:54     ` Steven Rostedt [this message]
2008-01-10 23:02     ` Steven Rostedt
2008-01-10 18:28   ` Sam Ravnborg
2008-01-10 19:10     ` Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 02/22 -v2] Annotate core code that should not be traced Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 03/22 -v2] x86_64: notrace annotations Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 04/22 -v2] add notrace annotations to vsyscall Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 05/22 -v2] add notrace annotations for NMI routines Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 06/22 -v2] mcount based trace in the form of a header file library Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 07/22 -v2] tracer add debugfs interface Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 08/22 -v2] mcount tracer output file Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 09/22 -v2] mcount tracer show task comm and pid Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 10/22 -v2] Add a symbol only trace output Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 11/22 -v2] Reset the tracer when started Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 12/22 -v2] separate out the percpu date into a percpu struct Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 13/22 -v2] handle accurate time keeping over long delays Steven Rostedt
2008-01-10  0:00   ` john stultz
2008-01-10  0:09     ` Steven Rostedt
2008-01-10 19:54     ` Tony Luck
2008-01-10 20:15       ` Steven Rostedt
2008-01-10 20:41         ` john stultz
2008-01-10 20:29       ` john stultz
2008-01-10 20:42         ` Mathieu Desnoyers
2008-01-10 21:25           ` john stultz
2008-01-10 22:00             ` Mathieu Desnoyers
2008-01-10 22:40               ` Steven Rostedt
2008-01-10 22:51               ` john stultz
2008-01-10 23:05                 ` john stultz
2008-01-10 21:33         ` [RFC PATCH 13/22 -v2] handle accurate time keeping over longdelays Luck, Tony
2008-01-10  0:19   ` [RFC PATCH 13/22 -v2] handle accurate time keeping over long delays john stultz
2008-01-10  0:25     ` Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 14/22 -v2] time keeping add cycle_raw for actual incrementation Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 15/22 -v2] initialize the clock source to jiffies clock Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 16/22 -v2] add get_monotonic_cycles Steven Rostedt
2008-01-10  3:28   ` Daniel Walker
2008-01-15 21:46   ` Mathieu Desnoyers
2008-01-15 22:01     ` Steven Rostedt
2008-01-15 22:03       ` Steven Rostedt
2008-01-15 22:08       ` Mathieu Desnoyers
2008-01-16  1:38         ` Steven Rostedt
2008-01-16  3:17           ` Mathieu Desnoyers
2008-01-16 13:17             ` Steven Rostedt
2008-01-16 14:56               ` Mathieu Desnoyers
2008-01-16 15:06                 ` Steven Rostedt
2008-01-16 15:28                   ` Mathieu Desnoyers
2008-01-16 15:58                     ` Steven Rostedt
2008-01-16 17:00                       ` Mathieu Desnoyers
2008-01-16 17:49                         ` Mathieu Desnoyers
2008-01-16 19:43                         ` Steven Rostedt
2008-01-16 20:17                           ` Mathieu Desnoyers
2008-01-16 20:45                             ` Tim Bird
2008-01-16 20:49                             ` Steven Rostedt
2008-01-17 20:08                             ` Steven Rostedt
2008-01-17 20:37                               ` Frank Ch. Eigler
2008-01-17 21:03                                 ` Steven Rostedt
2008-01-18 22:26                                   ` Mathieu Desnoyers
2008-01-18 22:49                                     ` Steven Rostedt
2008-01-18 23:19                                       ` Mathieu Desnoyers
2008-01-19  3:36                                         ` Frank Ch. Eigler
2008-01-19  3:55                                           ` Steven Rostedt
2008-01-19  4:23                                             ` Frank Ch. Eigler
2008-01-19 15:29                                               ` Mathieu Desnoyers
2008-01-19  3:32                                       ` Frank Ch. Eigler
2008-01-16 18:01                       ` Tim Bird
2008-01-16 22:36                 ` john stultz
2008-01-16 22:51                   ` john stultz
2008-01-16 23:33                     ` Steven Rostedt
2008-01-17  2:28                       ` john stultz
2008-01-17  2:40                         ` Mathieu Desnoyers
2008-01-17  2:50                           ` Mathieu Desnoyers
2008-01-17  3:02                             ` Steven Rostedt
2008-01-17  3:21                             ` Paul Mackerras
2008-01-17  3:39                               ` Steven Rostedt
2008-01-17  4:22                                 ` Mathieu Desnoyers
2008-01-17  4:25                                 ` Mathieu Desnoyers
2008-01-17  4:14                               ` Mathieu Desnoyers
2008-01-17 15:22                                 ` Steven Rostedt
2008-01-17 17:46                                 ` Linus Torvalds
2008-01-17  2:51                           ` Steven Rostedt
2008-01-16 23:39                     ` Mathieu Desnoyers
2008-01-16 23:50                       ` Steven Rostedt
2008-01-17  0:36                         ` Steven Rostedt
2008-01-17  0:33                       ` john stultz
2008-01-17  2:20                         ` Mathieu Desnoyers
2008-01-17  1:03                       ` Linus Torvalds
2008-01-17  1:35                         ` Mathieu Desnoyers
2008-01-17  2:20                       ` john stultz
2008-01-17  2:35                         ` Mathieu Desnoyers
2008-01-09 23:29 ` [RFC PATCH 17/22 -v2] Add timestamps to tracer Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 18/22 -v2] Sort trace by timestamp Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 19/22 -v2] speed up the output of the tracer Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 20/22 -v2] Add latency_trace format tor tracer Steven Rostedt
2008-01-10  3:41   ` Daniel Walker
2008-01-09 23:29 ` [RFC PATCH 21/22 -v2] Split out specific tracing functions Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 22/22 -v2] Trace irq disabled critical timings Steven Rostedt
2008-01-10  3:58   ` Daniel Walker
2008-01-10 14:45     ` Steven Rostedt

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