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

Michael Kerrisk (man-pages)
2015-02-26T07:51:17Z

Hi Stephane (and Jiri),

Ping!

Cheers,

Michael

On 02/17/2015 06:33 AM, Michael Kerrisk (man-pages) wrote:
> 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/