linux-kernel - Re: [PATCH 01/10] perf, trace: Remove IRQ-disable from perf/tracepoint interaction

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Date:	Sun, 23 May 2010 20:16:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/10] perf, trace: Remove IRQ-disable from
 perf/tracepoint interaction

On Sun, 2010-05-23 at 22:11 +1000, Paul Mackerras wrote:
> On Fri, May 21, 2010 at 11:02:02AM +0200, Peter Zijlstra wrote:
> 
> >  	entry = (struct trace_entry *)raw_data;
> > -	tracing_generic_entry_update(entry, *irq_flags, pc);
> > +	tracing_generic_entry_update(entry, regs->flags, pc);
> >  	entry->type = type;
> 
> This is breaking on powerpc -- we don't have a "flags" element in
> struct pt_regs.  What is it trying to do?  Get the interrupt enable
> state, as local_irq_save(flags) would provide?

Yes, I fouled that up.

On x86 perf_arch_fetch_caller_regs() stores pt_regs::flags, which is the
same as used in local_save_flags().

So to avoid another local_save_flags() for the ftrace code, I wanted to
reuse it, and totally forgot the !x86 side of things.

Possibly we could remove the local_save_flags() from the
perf_arch_fetch_caller_regs() as I'm not sure we actually use
pt_regs::flags (Frederic?) and leave the ftrace thing to use
local_save_flags().

Something like:


---
 arch/x86/kernel/cpu/perf_event.c |    1 -
 kernel/trace/trace_event_perf.c  |    4 +++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index fd4db0d..856aeeb 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1717,7 +1717,6 @@ void perf_arch_fetch_caller_regs(struct pt_regs *regs, unsigned long ip, int ski
 	 */
 	regs->bp = rewind_frame_pointer(skip + 1);
 	regs->cs = __KERNEL_CS;
-	local_save_flags(regs->flags);
 }
 
 unsigned long perf_instruction_pointer(struct pt_regs *regs)
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 26b8607..cb6f365 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -157,6 +157,7 @@ __kprobes void *perf_trace_buf_prepare(int size, unsigned short type,
 				       struct pt_regs *regs, int *rctxp)
 {
 	struct trace_entry *entry;
+	unsigned long flags;
 	char *raw_data;
 	int pc;
 
@@ -174,7 +175,8 @@ __kprobes void *perf_trace_buf_prepare(int size, unsigned short type,
 	memset(&raw_data[size - sizeof(u64)], 0, sizeof(u64));
 
 	entry = (struct trace_entry *)raw_data;
-	tracing_generic_entry_update(entry, regs->flags, pc);
+	local_save_flags(flags);
+	tracing_generic_entry_update(entry, flags, pc);
 	entry->type = type;
 
 	return raw_data;


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