linux-kernel - Re: [patch] perf_event_open.2: 3.19 PERF_SAMPLE_REGS

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Date:	Sat, 28 Feb 2015 23:26:05 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	linux-man@...r.kernel.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Stephane Eranian <eranian@...gle.com>, cebbert.lkml@...il.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	andi@...stfloor.org
Subject: Re: [patch] perf_event_open.2: 3.19 PERF_SAMPLE_REGS_INTR support

On Thu, Feb 12, 2015 at 12:33:09AM -0500, Vince Weaver wrote:
> 
> This manpage patch relates to the addition of PERF_SAMPLE_REGS_INTR
> support added in the following commit:

hi,
sorry for late response..

> 
>     perf_sample_regs_intr; Linux 3.19
> 	commit 60e2364e60e86e81bc6377f49779779e6120977f
> 	Author: Stephane Eranian <eranian@...gle.com>
> 
>             perf: Add ability to sample machine state on interrupt
> 
> 	Reviewed-by: Jiri Olsa <jolsa@...hat.com>
> 	Signed-off-by: Stephane Eranian <eranian@...gle.com>
> 	Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 	Cc: cebbert.lkml@...il.com
> 	Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> 	Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> 	Cc: linux-api@...r.kernel.org
> 	Link: http://lkml.kernel.org/r/1411559322-16548-2-git-send-email-eranian@google.com
> 	Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
> From what I can tell the primary difference between 
> PERF_SAMPLE_REGS_INTR and the existing PERF_SAMPLE_REGS_USER
> is that the new support will return kernel register values

correct

> (I assume that's not some sort of info leak?).
> 
> In theory also when precise_ip is set high enough you should
> get the PEBS register state rather than the PMU interrupt
> register state, but I was unable to construct a test case

yep, if precise_ip is set you'll get the registers values
from PEBS for PERF_SAMPLE_REGS_INTR set.. I dont think we
do this for PERF_SAMPLE_REGS_USER regs

> on a Haswell system where I got different values with
> precise_ip=0, precise_ip=2, or by using PERF_SAMPLE_REGS_USER
> instead.  Am I missing something about how to use this new 
> interface?

Could you please describe in more details what was your test doing?

the man page change below looks good to me

thanks,
jirka

> 
> Signed-off-by: Vince Weaver <vincent.weaver@...ne.edu>
> 
> diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
> index 39c8d8c..ca03928 100644
> --- a/man2/perf_event_open.2
> +++ b/man2/perf_event_open.2
> @@ -256,7 +256,7 @@ struct perf_event_attr {
>      __u32 sample_stack_user;    /* size of stack to dump on
>                                     samples */
>      __u32 __reserved_2;         /* Align to u64 */
> -
> +    __u64 sample_regs_intr;     /* regs to dump on samples */
>  };
>  .fi
>  .in
> @@ -350,6 +350,11 @@ and
>  .I sample_stack_user
>  in Linux 3.7.
>  .\" commit 1659d129ed014b715b0b2120e6fd929bdd33ed03
> +.B PERF_ATTR_SIZE_VER4
> +is 104 corresponding to the addition of
> +.I sample_regs_intr
> +in Linux 3.19.
> +.\" commit 60e2364e60e86e81bc6377f49779779e6120977f
>  .TP
>  .I "config"
>  This specifies which event you want, in conjunction with
> @@ -752,6 +757,23 @@ event must be measured or no values will be recorded.
>  Also note that some perf_event measurements, such as sampled
>  cycle counting, may cause extraneous aborts (by causing an
>  interrupt during a transaction).
> +.TP
> +.BR PERF_SAMPLE_REGS_INTR " (since Linux 3.19)"
> +.\" commit 60e2364e60e86e81bc6377f49779779e6120977f
> +Records a subset of the current CPU register state
> +as specified by
> +.IR sample_regs_intr .
> +Unlike
> +.B PERF_SAMPLE_REGS_USER
> +the register values will return kernel register
> +state if the overflow happened while kernel
> +code is running.
> +If the CPU supports hardware sampling of
> +register state (as does PEBS on x86) and
> +.I precise_ip
> +is set higher than zero then the register
> +values returned are those captured by
> +hardware.
>  .RE
>  .TP
>  .IR "read_format"
> @@ -1855,6 +1877,9 @@ struct {
>      u64   weight;     /* if PERF_SAMPLE_WEIGHT */
>      u64   data_src;   /* if PERF_SAMPLE_DATA_SRC */
>      u64   transaction;/* if PERF_SAMPLE_TRANSACTION */
> +    u64   abi;        /* if PERF_SAMPLE_REGS_INTR */
> +    u64   regs[weight(mask)];
> +                      /* if PERF_SAMPLE_REGS_INTR */
>  };
>  .fi
>  .RS 4
> @@ -2242,6 +2267,27 @@ the high 32 bits of the field by shifting right by
>  .B PERF_TXN_ABORT_SHIFT
>  and masking with
>  .BR PERF_TXN_ABORT_MASK .
> +.TP
> +.IR abi ", " regs[weight(mask)]
> +If
> +.B PERF_SAMPLE_REGS_INTR
> +is enabled, then the user CPU registers are recorded.
> +
> +The
> +.I abi
> +field is one of
> +.BR PERF_SAMPLE_REGS_ABI_NONE ", " PERF_SAMPLE_REGS_ABI_32 " or "
> +.BR PERF_SAMPLE_REGS_ABI_64 .
> +
> +The
> +.I regs
> +field is an array of the CPU registers that were specified by
> +the
> +.I sample_regs_intr
> +attr field.
> +The number of values is the number of bits set in the
> +.I sample_regs_intr
> +bit mask.
>  .RE
>  .TP
>  .B PERF_RECORD_MMAP2
> 
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