linux-kernel - Re: [RFC] perf: Delayed userspace unwind (Was: [PATCH v3 00/10] x86: ORC unwinder)

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Date:   Fri, 28 Jul 2017 16:21:30 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andres Freund <andres@...razel.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
        "H. Peter Anvin" <hpa@...or.com>, Mike Galbraith <efault@....de>,
        Arnaldo Carvalho de Melo <acme@...radead.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: Re: [RFC] perf: Delayed userspace unwind (Was: [PATCH v3 00/10] x86:
 ORC unwinder)

On Fri, Jul 28, 2017 at 04:13:25PM +0200, Jiri Olsa wrote:
> On Tue, Jul 25, 2017 at 01:55:12PM +0200, Peter Zijlstra wrote:
> 
> SNIP
> 
> >  
> > diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> > index 1b2be63c8528..c98a12f3592c 100644
> > --- a/kernel/events/callchain.c
> > +++ b/kernel/events/callchain.c
> > @@ -12,6 +12,7 @@
> >  #include <linux/perf_event.h>
> >  #include <linux/slab.h>
> >  #include <linux/sched/task_stack.h>
> > +#include <linux/task_work.h>
> >  
> >  #include "internal.h"
> >  
> > @@ -178,19 +179,94 @@ put_callchain_entry(int rctx)
> >  	put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
> >  }
> >  
> > +static struct perf_callchain_entry __empty = { .nr = 0, };
> > +
> > +static void perf_callchain_work(struct callback_head *work)
> > +{
> > +	struct perf_event *event = container_of(work, struct perf_event, pending_callchain);
> > +	struct perf_output_handle handle;
> > +	struct perf_sample_data sample;
> > +	size_t size;
> > +	int ret;
> > +
> > +	struct {
> > +		struct perf_event_header	header;
> > +	} callchain_event = {
> > +		.header = {
> > +			.type = PERF_RECORD_CALLCHAIN,
> > +			.misc = 0,
> > +			.size = sizeof(callchain_event),
> > +		},
> > +	};
> 
> how about we make this generic for all user space sample_type?
> 
> I think we could certainly use it for PERF_SAMPLE_STACK_USER,
> maybe PERF_SAMPLE_REGS_USER would also help.. just a little ;-)
> 
> I'll check on that

Right, so I put all the magic in the callchain code itself, which would
make that a wee bit harder. But yes, putting all the USER stuff in there
makes sense.