Re: [PATCH] perf kvm record: Change the default value of perf_guest to 0.

Re: [PATCH] perf kvm record: Change the default value of perf_guest to 0.

[David Ahern]

On 11/14/13, 2:51 PM, Dongsheng Yang wrote:
> Currently, we can not record the event counters of host to perf.data.host.
> Example:
>     perf kvm --host record -a sleep 1
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.625 MB perf.data.guest (~27290 samples) ]

perf kvm by definition wants --guest enabled. Host profiling is done 
with just 'perf record'; no need for the kvm layer at all. If you really 
want to go through perf-kvm to record host events disable guest actions:

$ perf kvm --host --no-guest record -a sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.029 MB perf.data.host (~1255 samples) ]


David

[PATCH] perf kvm record: Change the default value of perf_guest to 0.

[Dongsheng Yang]

Currently, we can not record the event counters of host to perf.data.host.
Example:
   perf kvm --host record -a sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.625 MB perf.data.guest (~27290 samples) ]

The record file is named 'perf.data.kvm' and the content of it is about host
and guest. But we expect the record file is named 'perf.data.host' with the
counters only about host.

The issue was introduced by 1aed267(perf kvm: Do guest-only counting by default).

Actually, the following code can make sure that do guest-only by default:
    if (!perf_host)
        perf_guest = 1;

So, changing the default value from 0 to 1 is not a good idea, it prevents
us from getting 'perf.data.host' by '--host'.

With this patch applied, the behavior of perf-kvm is shown as below:
	* Default 	 -> perf.data.guest
	* --host  	 -> perf.data.host
	* --guest 	 -> perf.data.guest
	* --host --guest -> perf.data.kvm

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
---
 tools/perf/builtin-kvm.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tools/perf/builtin-kvm.c b/tools/perf/builtin-kvm.c
index cd9f920..eac8269 100644
--- a/tools/perf/builtin-kvm.c
+++ b/tools/perf/builtin-kvm.c
@@ -1709,8 +1709,7 @@ int cmd_kvm(int argc, const char **argv, const char *prefix __maybe_unused)
 		NULL
 	};
 
-	perf_host  = 0;
-	perf_guest = 1;
+	perf_host = perf_guest = 0;
 
 	argc = parse_options(argc, argv, kvm_options, kvm_usage,
 			PARSE_OPT_STOP_AT_NON_OPTION);
-- 
1.8.2.1

Re: [PATCH] perf kvm record: Change the default value of perf_guest to 0.

[Dongsheng Yang]

Hi David:

On 11/14/2013 03:38 PM, David Ahern wrote:
> On 11/14/13, 2:51 PM, Dongsheng Yang wrote:
>> Currently, we can not record the event counters of host to 
>> perf.data.host.
>> Example:
>>     perf kvm --host record -a sleep 1
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 0.625 MB perf.data.guest (~27290 
>> samples) ]
>
> perf kvm by definition wants --guest enabled. Host profiling is done 
> with just 'perf record'; no need for the kvm layer at all. If you 
> really want to go through perf-kvm to record host events disable guest 
> actions:
>
> $ perf kvm --host --no-guest record -a sleep 1
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.029 MB perf.data.host (~1255 
> samples) ]
>
>
> David

Thanx for your reply ! It makes sense.

[PATCH] perf kvm record: Change the default value of perf_guest to 0.

[Dongsheng Yang]

Currently, we can not record the event counters of host to perf.data.host.
Example:
   perf kvm --host record -a sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.625 MB perf.data.guest (~27290 samples) ]

The record file is named 'perf.data.kvm' and the content of it is about host
and guest. But we expect the record file is named 'perf.data.host' with the
counters only about host.

The issue was introduced by 1aed267(perf kvm: Do guest-only counting by default).

Actually, the following code can make sure that do guest-only by default:
    if (!perf_host)
        perf_guest = 1;

So, changing the default value from 0 to 1 is not a good idea, it prevents
us from getting 'perf.data.host' by '--host'.

With this patch applied, the behavior of perf-kvm is shown as below:
	* Default 	 -> perf.data.guest
	* --host  	 -> perf.data.host
	* --guest 	 -> perf.data.guest
	* --host --guest -> perf.data.kvm

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
---
 tools/perf/builtin-kvm.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tools/perf/builtin-kvm.c b/tools/perf/builtin-kvm.c
index cd9f920..eac8269 100644
--- a/tools/perf/builtin-kvm.c
+++ b/tools/perf/builtin-kvm.c
@@ -1709,8 +1709,7 @@ int cmd_kvm(int argc, const char **argv, const char *prefix __maybe_unused)
 		NULL
 	};
 
-	perf_host  = 0;
-	perf_guest = 1;
+	perf_host = perf_guest = 0;
 
 	argc = parse_options(argc, argv, kvm_options, kvm_usage,
 			PARSE_OPT_STOP_AT_NON_OPTION);
-- 
1.8.2.1