[RFC PATCH] perf tools: Don't set inherit bit for system wide evsel

[RFC PATCH] perf tools: Don't set inherit bit for system wide evsel

[Wang Nan]

Inherit bit is useless for a system wide evsel [1]. Further kernel
improvements are giving more constrain [2] on inherit events. This
patch set inherit bit to 0 to avoid potential constrains.

[1] http://lkml.kernel.org/r/20151022124142.GQ17308@twins.programming.kicks-ass.net
[2] http://lkml.kernel.org/r/1445559014-4667-1-git-send-email-ast@kernel.org

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Li Zefan <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/n/ebpf-0tgilipxoo6fiebcxu3ft866@git.kernel.org
---

evsel->system_wide doesn't correct reflect whether this evsel is system
wide or not, so checks pid when invoking perf_event_open, and it is
always correct.

---
 tools/perf/util/evsel.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 5566b16..e2d6c9a 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1337,6 +1337,7 @@ retry_sample_id:
 
 		for (thread = 0; thread < nthreads; thread++) {
 			int group_fd;
+			struct perf_event_attr attr;
 
 			if (!evsel->cgrp && !evsel->system_wide)
 				pid = thread_map__pid(threads, thread);
@@ -1346,7 +1347,10 @@ retry_open:
 			pr_debug2("sys_perf_event_open: pid %d  cpu %d  group_fd %d  flags %#lx\n",
 				  pid, cpus->map[cpu], group_fd, flags);
 
-			FD(evsel, cpu, thread) = sys_perf_event_open(&evsel->attr,
+			attr = evsel->attr;
+			if (pid == -1)
+				attr.inherit = 0;
+			FD(evsel, cpu, thread) = sys_perf_event_open(&attr,
 								     pid,
 								     cpus->map[cpu],
 								     group_fd, flags);
-- 
1.8.3.4

Re: [RFC PATCH] perf tools: Don't set inherit bit for system wide evsel

[Arnaldo Carvalho de Melo]

Em Fri, Oct 23, 2015 at 10:43:49AM +0000, Wang Nan escreveu:
> Inherit bit is useless for a system wide evsel [1]. Further kernel
> improvements are giving more constrain [2] on inherit events. This
> patch set inherit bit to 0 to avoid potential constrains.
> 
> [1] http://lkml.kernel.org/r/20151022124142.GQ17308@twins.programming.kicks-ass.net
> [2] http://lkml.kernel.org/r/1445559014-4667-1-git-send-email-ast@kernel.org
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Alexei Starovoitov <ast@plumgrid.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Li Zefan <lizefan@huawei.com>
> Cc: pi3orama@163.com
> Link: http://lkml.kernel.org/n/ebpf-0tgilipxoo6fiebcxu3ft866@git.kernel.org
> ---
> 
> evsel->system_wide doesn't correct reflect whether this evsel is system
> wide or not, so checks pid when invoking perf_event_open, and it is
> always correct.

Can't we do this at perf_evlist__config() or perf_evsel__config() time?

We have record_opts at perf_evsel__config() time and I think we should
leave changing the attr at perf_evsel__open() time for feature
fallbacks, i.e. something we will only know when trying to use, which is
different from this inherit-on-syswide case, that we know far in advance
we will not need.

- Arnaldo
 
> ---
>  tools/perf/util/evsel.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 5566b16..e2d6c9a 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1337,6 +1337,7 @@ retry_sample_id:
>  
>  		for (thread = 0; thread < nthreads; thread++) {
>  			int group_fd;
> +			struct perf_event_attr attr;
>  
>  			if (!evsel->cgrp && !evsel->system_wide)
>  				pid = thread_map__pid(threads, thread);
> @@ -1346,7 +1347,10 @@ retry_open:
>  			pr_debug2("sys_perf_event_open: pid %d  cpu %d  group_fd %d  flags %#lx\n",
>  				  pid, cpus->map[cpu], group_fd, flags);
>  
> -			FD(evsel, cpu, thread) = sys_perf_event_open(&evsel->attr,
> +			attr = evsel->attr;
> +			if (pid == -1)
> +				attr.inherit = 0;
> +			FD(evsel, cpu, thread) = sys_perf_event_open(&attr,
>  								     pid,
>  								     cpus->map[cpu],
>  								     group_fd, flags);
> -- 
> 1.8.3.4

Re: [RFC PATCH] perf tools: Don't set inherit bit for system wide evsel

[pi3orama]

发自我的 iPhone

> 在 2015年10月23日，下午9:51，Arnaldo Carvalho de Melo <acme@kernel.org> 写道：
> 
> Em Fri, Oct 23, 2015 at 10:43:49AM +0000, Wang Nan escreveu:
>> Inherit bit is useless for a system wide evsel [1]. Further kernel
>> improvements are giving more constrain [2] on inherit events. This
>> patch set inherit bit to 0 to avoid potential constrains.
>> 
>> [1] http://lkml.kernel.org/r/20151022124142.GQ17308@twins.programming.kicks-ass.net
>> [2] http://lkml.kernel.org/r/1445559014-4667-1-git-send-email-ast@kernel.org
>> 
>> Signed-off-by: Wang Nan <wangnan0@huawei.com>
>> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
>> Cc: Alexei Starovoitov <ast@plumgrid.com>
>> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
>> Cc: Li Zefan <lizefan@huawei.com>
>> Cc: pi3orama@163.com
>> Link: http://lkml.kernel.org/n/ebpf-0tgilipxoo6fiebcxu3ft866@git.kernel.org
>> ---
>> 
>> evsel->system_wide doesn't correct reflect whether this evsel is system
>> wide or not, so checks pid when invoking perf_event_open, and it is
>> always correct.
> 
> Can't we do this at perf_evlist__config() or perf_evsel__config() time?

perf_evlist_config() is excluded because perf record doesn't use it.

> 
> We have record_opts at perf_evsel__config() time and I think we should
> leave changing the attr at perf_evsel__open() time for feature
> fallbacks, i.e. something we will only know when trying to use, which is
> different from this inherit-on-syswide case, that we know far in advance
> we will not need.

I tried to set this bit based on evsel->system_wide but it seems not reliable
as it should be, so I was wondering whether it is designed for other use. I will look
into this next week.

Thank you.
> 
> - Arnaldo
> 
>> ---
>> tools/perf/util/evsel.c | 6 +++++-
>> 1 file changed, 5 insertions(+), 1 deletion(-)
>> 
>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>> index 5566b16..e2d6c9a 100644
>> --- a/tools/perf/util/evsel.c
>> +++ b/tools/perf/util/evsel.c
>> @@ -1337,6 +1337,7 @@ retry_sample_id:
>> 
>>        for (thread = 0; thread < nthreads; thread++) {
>>            int group_fd;
>> +            struct perf_event_attr attr;
>> 
>>            if (!evsel->cgrp && !evsel->system_wide)
>>                pid = thread_map__pid(threads, thread);
>> @@ -1346,7 +1347,10 @@ retry_open:
>>            pr_debug2("sys_perf_event_open: pid %d  cpu %d  group_fd %d  flags %#lx\n",
>>                  pid, cpus->map[cpu], group_fd, flags);
>> 
>> -            FD(evsel, cpu, thread) = sys_perf_event_open(&evsel->attr,
>> +            attr = evsel->attr;
>> +            if (pid == -1)
>> +                attr.inherit = 0;
>> +            FD(evsel, cpu, thread) = sys_perf_event_open(&attr,
>>                                     pid,
>>                                     cpus->map[cpu],
>>                                     group_fd, flags);
>> -- 
>> 1.8.3.4

Re: [RFC PATCH] perf tools: Don't set inherit bit for system wide evsel

[Arnaldo Carvalho de Melo]

Em Fri, Oct 23, 2015 at 09:58:20PM +0800, pi3orama escreveu:
> 
> 
> 发自我的 iPhone
> 
> > 在 2015年10月23日，下午9:51，Arnaldo Carvalho de Melo <acme@kernel.org> 写道：
> > 
> > Em Fri, Oct 23, 2015 at 10:43:49AM +0000, Wang Nan escreveu:
> >> Inherit bit is useless for a system wide evsel [1]. Further kernel
> >> improvements are giving more constrain [2] on inherit events. This
> >> patch set inherit bit to 0 to avoid potential constrains.
> >> 
> >> [1] http://lkml.kernel.org/r/20151022124142.GQ17308@twins.programming.kicks-ass.net
> >> [2] http://lkml.kernel.org/r/1445559014-4667-1-git-send-email-ast@kernel.org
> >> 
> >> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> >> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> >> Cc: Alexei Starovoitov <ast@plumgrid.com>
> >> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> >> Cc: Li Zefan <lizefan@huawei.com>
> >> Cc: pi3orama@163.com
> >> Link: http://lkml.kernel.org/n/ebpf-0tgilipxoo6fiebcxu3ft866@git.kernel.org
> >> ---
> >> 
> >> evsel->system_wide doesn't correct reflect whether this evsel is system
> >> wide or not, so checks pid when invoking perf_event_open, and it is
> >> always correct.
> > 
> > Can't we do this at perf_evlist__config() or perf_evsel__config() time?
> 
> perf_evlist_config() is excluded because perf record doesn't use it.

Yeah, we need to make it use it :-\
 
> > We have record_opts at perf_evsel__config() time and I think we should
> > leave changing the attr at perf_evsel__open() time for feature
> > fallbacks, i.e. something we will only know when trying to use, which is
> > different from this inherit-on-syswide case, that we know far in advance
> > we will not need.
> 
> I tried to set this bit based on evsel->system_wide but it seems not reliable
> as it should be, so I was wondering whether it is designed for other use. I will look
> into this next week.

Ok, thanks in advance, lemme go back looking at eBPF :-)

- Arnaldo

Re: [RFC PATCH] perf tools: Don't set inherit bit for system wide evsel

[Wangnan (F)]

On 2015/10/24 0:17, Arnaldo Carvalho de Melo wrote:
> Em Fri, Oct 23, 2015 at 09:58:20PM +0800, pi3orama escreveu:
>>
>> 发自我的 iPhone
>>
>>> 在 2015年10月23日，下午9:51，Arnaldo Carvalho de Melo <acme@kernel.org> 写道：
>>>
>>> Em Fri, Oct 23, 2015 at 10:43:49AM +0000, Wang Nan escreveu:
>>>> Inherit bit is useless for a system wide evsel [1]. Further kernel
>>>> improvements are giving more constrain [2] on inherit events. This
>>>> patch set inherit bit to 0 to avoid potential constrains.
>>>>
>>>> [1] http://lkml.kernel.org/r/20151022124142.GQ17308@twins.programming.kicks-ass.net
>>>> [2] http://lkml.kernel.org/r/1445559014-4667-1-git-send-email-ast@kernel.org
>>>>
>>>> Signed-off-by: Wang Nan <wangnan0@huawei.com>
>>>> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
>>>> Cc: Alexei Starovoitov <ast@plumgrid.com>
>>>> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
>>>> Cc: Li Zefan <lizefan@huawei.com>
>>>> Cc: pi3orama@163.com
>>>> Link: http://lkml.kernel.org/n/ebpf-0tgilipxoo6fiebcxu3ft866@git.kernel.org
>>>> ---
>>>>
>>>> evsel->system_wide doesn't correct reflect whether this evsel is system
>>>> wide or not, so checks pid when invoking perf_event_open, and it is
>>>> always correct.
>>> Can't we do this at perf_evlist__config() or perf_evsel__config() time?
>> perf_evlist_config() is excluded because perf record doesn't use it.
> Yeah, we need to make it use it :-\

Its my fault that perf record *does* use perf_evlist__config(), but 
'perf stat'
doesn't.

>   
>>> We have record_opts at perf_evsel__config() time and I think we should
>>> leave changing the attr at perf_evsel__open() time for feature
>>> fallbacks, i.e. something we will only know when trying to use, which is
>>> different from this inherit-on-syswide case, that we know far in advance
>>> we will not need.
>> I tried to set this bit based on evsel->system_wide but it seems not reliable
>> as it should be, so I was wondering whether it is designed for other use. I will look
>> into this next week.

evsel->system_wide is introduced by commit 
bf8e8f4b832972c76d64ab2e2837a48397144887
(perf evlist: Add 'system_wide' option), but Adrian only introduced a 
new field
into perf, doesn't really make it active. Until now the only user of it is
arch/x86/util/intel-pt.c, but I'm not very sure the reason for IPT to 
use that
field.

If I understand correctly, it should be okay for a normal system wide 
evsel to have
this var set. I'll try another RFC for it.

Thank you.

> Ok, thanks in advance, lemme go back looking at eBPF :-)
>
> - Arnaldo

Re: [RFC PATCH] perf tools: Don't set inherit bit for system wide evsel

[Adrian Hunter]

On 26/10/15 11:08, Wangnan (F) wrote:
> 
> 
> On 2015/10/24 0:17, Arnaldo Carvalho de Melo wrote:
>> Em Fri, Oct 23, 2015 at 09:58:20PM +0800, pi3orama escreveu:
>>>
>>> 发自我的 iPhone
>>>
>>>> 在 2015年10月23日，下午9:51，Arnaldo Carvalho de Melo <acme@kernel.org>
>>>> 写道：
>>>>
>>>> Em Fri, Oct 23, 2015 at 10:43:49AM +0000, Wang Nan escreveu:
>>>>> Inherit bit is useless for a system wide evsel [1]. Further kernel
>>>>> improvements are giving more constrain [2] on inherit events. This
>>>>> patch set inherit bit to 0 to avoid potential constrains.
>>>>>
>>>>> [1]
>>>>> http://lkml.kernel.org/r/20151022124142.GQ17308@twins.programming.kicks-ass.net
>>>>>
>>>>> [2]
>>>>> http://lkml.kernel.org/r/1445559014-4667-1-git-send-email-ast@kernel.org
>>>>>
>>>>> Signed-off-by: Wang Nan <wangnan0@huawei.com>
>>>>> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
>>>>> Cc: Alexei Starovoitov <ast@plumgrid.com>
>>>>> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
>>>>> Cc: Li Zefan <lizefan@huawei.com>
>>>>> Cc: pi3orama@163.com
>>>>> Link:
>>>>> http://lkml.kernel.org/n/ebpf-0tgilipxoo6fiebcxu3ft866@git.kernel.org
>>>>> ---
>>>>>
>>>>> evsel->system_wide doesn't correct reflect whether this evsel is system
>>>>> wide or not, so checks pid when invoking perf_event_open, and it is
>>>>> always correct.
>>>> Can't we do this at perf_evlist__config() or perf_evsel__config() time?
>>> perf_evlist_config() is excluded because perf record doesn't use it.
>> Yeah, we need to make it use it :-\
> 
> Its my fault that perf record *does* use perf_evlist__config(), but 'perf stat'
> doesn't.
> 
>>  
>>>> We have record_opts at perf_evsel__config() time and I think we should
>>>> leave changing the attr at perf_evsel__open() time for feature
>>>> fallbacks, i.e. something we will only know when trying to use, which is
>>>> different from this inherit-on-syswide case, that we know far in advance
>>>> we will not need.
>>> I tried to set this bit based on evsel->system_wide but it seems not
>>> reliable
>>> as it should be, so I was wondering whether it is designed for other use.
>>> I will look
>>> into this next week.
> 
> evsel->system_wide is introduced by commit
> bf8e8f4b832972c76d64ab2e2837a48397144887
> (perf evlist: Add 'system_wide' option), but Adrian only introduced a new field
> into perf, doesn't really make it active. Until now the only user of it is
> arch/x86/util/intel-pt.c, but I'm not very sure the reason for IPT to use that
> field.
> 
> If I understand correctly, it should be okay for a normal system wide evsel
> to have
> this var set. I'll try another RFC for it.

evsel->system_wide is for mixing evsels that aren't system-wide with ones
that are.

It might work to set it for all system-wide evsels but you will have to
check the code and test it, because that would be using it in a new way
that has never been tested.

Re: [RFC PATCH] perf tools: Don't set inherit bit for system wide evsel

[Wangnan (F)]

On 2015/10/26 17:25, Adrian Hunter wrote:
> On 26/10/15 11:08, Wangnan (F) wrote:
>>
>> evsel->system_wide is introduced by commit
>> bf8e8f4b832972c76d64ab2e2837a48397144887
>> (perf evlist: Add 'system_wide' option), but Adrian only introduced a new field
>> into perf, doesn't really make it active. Until now the only user of it is
>> arch/x86/util/intel-pt.c, but I'm not very sure the reason for IPT to use that
>> field.
>>
>> If I understand correctly, it should be okay for a normal system wide evsel
>> to have
>> this var set. I'll try another RFC for it.
> evsel->system_wide is for mixing evsels that aren't system-wide with ones
> that are.
>
> It might work to set it for all system-wide evsels but you will have to
> check the code and test it, because that would be using it in a new way
> that has never been tested.

I have check all occurance of system_wide I can found and found
only one behavior change which I believe should be okay. Please
have a look at [1].

Thank you.

[1] 
http://lkml.kernel.org/g/1445859720-146146-1-git-send-email-wangnan0@huawei.com