Re: [PATCH 3/5] perf tools: Update the Document for perf kvm record for new behavior.

[Arnaldo Carvalho de Melo <acme@ghostprotocols.net>]

Em Wed, Dec 04, 2013 at 05:56:41PM -0500, Dongsheng Yang escreveu:
> As we have changed the default behavior of perf kvm to --guest enabled,
> the document about perf kvm record is outdated. This patch update it to
> show the correct output with --host/--guest/neither/both of them.
 
> +++ b/tools/perf/Documentation/perf-kvm.txt
> @@ -24,10 +24,17 @@ There are a couple of variants of perf kvm:
>    of an arbitrary workload.
  
>    'perf kvm record <command>' to record the performance counter profile
> -  of an arbitrary workload and save it into a perf data file. If both
> -  --host and --guest are input, the perf data file name is perf.data.kvm.
> -  If there is  no --host but --guest, the file name is perf.data.guest.
> -  If there is no --guest but --host, the file name is perf.data.host.
> +  of an arbitrary workload and save it into a perf data file. We set the
> +  default behavior of perf kvm as --guest, so if neither --host nor --guest
> +  is input, the perf data file name is perf.data.guest. If --host is input,
> +  the perf data file name is perf.data.kvm. If you want to record data into
> +  perf.data.host, please input --host --no-guest. The behaviors are shown as
> +  following:

Perhaps this is clearer:

"Use 'perf kvm record <command>' to record the a profile of an arbitrary
workload and save it into a perf.data file. The default is to record
guest samples, use --host to ask for just host samples or both --guest
and --host for both kinds of samples to be taken."

Argh, then I wonder why do we have --guest if the only possibility,
according to the text above, is for it to be used in the --no-guest
variant, is that the case?

Do we really, really need to have those .host or .guest or .kvm filename
suffixes?

Can't we have this somehow encoded in the perf.data file header and show
it when doing a report? humm, it is already, and we can see it already
in 'perf evlist':

[root@ssdandy ~]# perf kvm record -a
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 1.489 MB perf.data.guest (~65058 samples) ]
[root@ssdandy ~]# perf evlist
raw_syscalls:sys_enter
raw_syscalls:sys_exit
[root@ssdandy ~]# perf evlist -v
raw_syscalls:sys_enter: sample_freq=1, type: 2, config: 41, size: 96,
sample_type: IP|TID|TIME|CALLCHAIN|ID|CPU|PERIOD|RAW, read_format: ID,
disabled: 1, inherit: 1, mmap: 1, comm: 1, enable_on_exec: 1,
sample_id_all: 1, exclude_guest: 1
raw_syscalls:sys_exit: sample_freq=1, type: 2, config: 40, size: 96,
sample_type: IP|TID|TIME|CALLCHAIN|ID|CPU|PERIOD|RAW, read_format: ID,
disabled: 1, inherit: 1, enable_on_exec: 1, sample_id_all: 1,
exclude_guest: 1
[root@ssdandy ~]#

Humm, strange, the exclude_guest bit is set, which doesn't look like it
matches that text...

Lemme try explicitely using --guest and --host:

[root@ssdandy ~]# perf kvm --guest record sleep 2
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.012 MB perf.data.guest (~532 samples) ]
[root@ssdandy ~]# perf evlist -v
raw_syscalls:sys_enter: sample_freq=1, type: 2, config: 41, size: 96, sample_type: IP|TID|TIME|CALLCHAIN|ID|CPU|PERIOD|RAW, read_format: ID, disabled: 1, inherit: 1, mmap: 1, comm: 1, enable_on_exec: 1, sample_id_all: 1, exclude_guest: 1
raw_syscalls:sys_exit: sample_freq=1, type: 2, config: 40, size: 96, sample_type: IP|TID|TIME|CALLCHAIN|ID|CPU|PERIOD|RAW, read_format: ID, disabled: 1, inherit: 1, enable_on_exec: 1, sample_id_all: 1, exclude_guest: 1
[root@ssdandy ~]#

exclude_guest still there...

Then:

[root@ssdandy ~]# perf kvm --host record sleep 2
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.012 MB perf.data.kvm (~544 samples) ]
[root@ssdandy ~]# perf evlist -v
raw_syscalls:sys_enter: sample_freq=1, type: 2, config: 41, size: 96, sample_type: IP|TID|TIME|CALLCHAIN|ID|CPU|PERIOD|RAW, read_format: ID, disabled: 1, inherit: 1, mmap: 1, comm: 1, enable_on_exec: 1, sample_id_all: 1, exclude_guest: 1
raw_syscalls:sys_exit: sample_freq=1, type: 2, config: 40, size: 96, sample_type: IP|TID|TIME|CALLCHAIN|ID|CPU|PERIOD|RAW, read_format: ID, disabled: 1, inherit: 1, enable_on_exec: 1, sample_id_all: 1, exclude_guest: 1
[root@ssdandy ~]# 

Still there... oops, I've been just bitten by this odd suffixes convention,
as 'perf evlist', like all other tools, by default will look at 'perf.data', not
the 'perf kvm' convention...

So again:

[root@ssdandy ~]# perf kvm --guest record -a
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 1.060 MB perf.data.guest (~46303 samples) ]
[root@ssdandy ~]# ls -lart perf.data* | tail -1
-rw-------. 1 root root 1113684 Dec  4 11:11 perf.data.guest
[root@ssdandy ~]# perf evlist -v -i perf.data.guest
cycles: sample_freq=4000, size: 96, sample_type: IP|TID|TIME|CPU|PERIOD, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, sample_id_all: 1, exclude_host: 1
[root@ssdandy ~]# 

Matches the documentation, i.e. perf_event_attr.exclude_guest is not set,
meaning --guest, and .exclude_host is set, ok.

[root@ssdandy ~]# perf kvm --host record sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.013 MB perf.data.kvm (~554 samples) ]
[root@ssdandy ~]# ls -lart perf.data* | tail -1
-rw-------. 1 root root   15976 Dec  4 11:13 perf.data.kvm
[root@ssdandy ~]# perf evlist -v -i perf.data.kvm
cycles: sample_freq=4000, size: 96, sample_type: IP|TID|TIME|PERIOD, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, sample_id_all: 1
[root@ssdandy ~]#

Yes, 'perf kvm record --host' actually means: "perf kvm --host --guest', as
both exclude_{host,guest} are zeroed.

[root@ssdandy ~]# perf kvm --host --no-guest record sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.013 MB perf.data.host (~552 samples) ]
[root@ssdandy ~]# ls -lart perf.data* | tail -1
-rw-------. 1 root root   15904 Dec  4 11:14 perf.data.host
[root@ssdandy ~]# perf evlist -v -i perf.data.host
cycles: sample_freq=4000, size: 96, sample_type: IP|TID|TIME|PERIOD, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, sample_id_all: 1, exclude_guest: 1
[root@ssdandy ~]# 

Seems all ok, just not immediately intuitive.

I would expect one to do: (yeah, there was a discussion long ago, can't
remember the details right now, should have paid more attention at the
time :-\)

perf kvm record <target> 

to mean:

perf kvm record --host --guest <target>

and generate a perf.data file, just like all other tools.

What about 'perf kvm report', I think one will have to point it to the
right file to use, using -i, right? So doing it at 'perf kvm record'
explicitely as well will reduce confusion and make it behave just like
all the other tools?

Comments?

- Arnaldo

> +    Default('')         ->  perf.data.guest
> +    --host              ->  perf.data.kvm
> +    --guest             ->  perf.data.guest
> +    --host --guest      ->  perf.data.kvm
> +    --host --no-guest   ->  perf.data.host
>  
>    'perf kvm report' to display the performance counter profile information
>    recorded via perf kvm record.
> -- 
> 1.8.2.1