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

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Message-ID: <20100524113104.GA5325@nowhere>
Date:	Mon, 24 May 2010 13:31:09 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	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, May 23, 2010 at 08:16:27PM +0200, Peter Zijlstra wrote:
> 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().


It was an anticipation for further uses. But since further are not
appearing, you can safely remove it.


Thanks.

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