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 16:13:25 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 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

jirka