Re: [patch] perf_event_open.2: 3.19 PERF_SAMPLE_REGS_INTR support

Michael Kerrisk (man-pages)
2015-02-17T05:33:32Z

Hi Stephane (and Jiri),

Would you be willing to review/comment on Vince's patch, please.

Cheers,

Michael

On 02/12/2015 06:33 AM, Vince Weaver wrote:
>
> This manpage patch relates to the addition of PERF_SAMPLE_REGS_INTR
> support added in the following commit:
>
> perf_sample_regs_intr; Linux 3.19
> commit 60e2364e60e86e81bc6377f49779779e6120977f
> Author: Stephane Eranian <eranian@google.com>
>
> perf: Add ability to sample machine state on interrupt
>
> Reviewed-by: Jiri Olsa <jolsa@redhat.com>
> Signed-off-by: Stephane Eranian <eranian@google.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: cebbert.lkml@gmail.com
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: linux-api@vger.kernel.org
> Link: http://lkml.kernel.org/r/1411559322-16548-2-git-send-email-eranian@google.com
> Signed-off-by: Ingo Molnar <mingo@kernel.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
> (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
> 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?
>
> Signed-off-by: Vince Weaver <vincent.weaver@maine.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
>
>

--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/