linux-kernel - Re: [PATCH 1/8] perf: Add PERF_SAMPLE_PHYS

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Date:	Thu, 7 Jan 2016 09:33:19 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	kan.liang@...el.com
Cc:	peterz@...radead.org, acme@...nel.org, eranian@...gle.com,
	ak@...ux.intel.com, jolsa@...nel.org, namhyung@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] perf: Add PERF_SAMPLE_PHYS_ADDR

On Wed, Jan 06, 2016 at 06:04:30AM -0500, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> For understanding how the workload maps to memory channels and hardware
> behavior, it's useful to collect address maps with physical addresses.
> This is not intended for detecting page sharing (which can be already
> done using the mmap inode), but for lower level hardware behavior
> studies.
> Perf supports load latency/DLA which can only collect virtual addresses.
> This patch add a new sample type PERF_SAMPLE_PHYS_ADDR to expose the
> physical addresses.
> For kernel direct mapping addresses, the patch uses virt_to_phys to
> convert the virtual addresses from DLA to physical address.
> For user virtual addresses, __get_user_pages_fast is used to walk the
> pages tables for user physical address.
> This does not work for vmalloc addresses. Right now these are not
> resolved, but code to do that could be added.
> For security, the physical address can only be exposed to root or
> privileged user.
> 
> Signed-off-by: Kan Liang <kan.liang@...el.com>
> ---
>  arch/x86/kernel/cpu/perf_event.h          |  2 +-
>  arch/x86/kernel/cpu/perf_event_intel_ds.c | 23 +++++++++++++++++++++++
>  include/linux/perf_event.h                |  3 +++
>  include/uapi/linux/perf_event.h           |  4 +++-
>  kernel/events/core.c                      | 11 +++++++++++
>  5 files changed, 41 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
> index 799e6bd..164de68 100644
> --- a/arch/x86/kernel/cpu/perf_event.h
> +++ b/arch/x86/kernel/cpu/perf_event.h
> @@ -90,7 +90,7 @@ struct amd_nb {
>  	(PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_ADDR | \
>  	PERF_SAMPLE_ID | PERF_SAMPLE_CPU | PERF_SAMPLE_STREAM_ID | \
>  	PERF_SAMPLE_DATA_SRC | PERF_SAMPLE_IDENTIFIER | \
> -	PERF_SAMPLE_TRANSACTION)
> +	PERF_SAMPLE_TRANSACTION | PERF_SAMPLE_PHYS_ADDR)

could you please add some probe code to detect kernel
support, so we get some sensible error message

[jolsa@...va perf]$ ./perf mem -p record ls
Error:
The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (cpu/mem-loads/pp).
/bin/dmesg may provide additional information.
No CONFIG_PERF_EVENTS=y kernel support configured?

thanks,
jirka
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