linux-kernel - Re: [PATCH v3] perf parse-events: Set exclude

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Date:   Wed, 19 Aug 2020 11:05:05 +0800
From:   Like Xu <like.xu@...ux.intel.com>
To:     "Jin, Yao" <yao.jin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     jolsa@...nel.org, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v3] perf parse-events: Set exclude_guest=1 for user-space
 counting

Hi Arnaldo,

On 2020/8/17 10:32, Jin, Yao wrote:
> Hi Arnaldo,
> 
> On 8/14/2020 8:47 PM, Arnaldo Carvalho de Melo wrote:
>> Em Fri, Aug 14, 2020 at 09:21:20AM +0800, Jin Yao escreveu:
>>> Currently if we run 'perf record -e cycles:u', exclude_guest=0.
>>>
>>> But it doesn't make sense in most cases that we request for
>>> user-space counting but we also get the guest report.
>>>
>>> Of course, we also need to consider perf kvm usage case that
>>> authorized perf users on the host may only want to count guest
>>> user space events. For example,
>>>
>>> perf kvm --guest record -e cycles:u
>> Ok, probably this works, but what if I want to record guest user samples
>> without using 'perf kvm'?
>>
>> Can we have a 'U' modifier, perhaps, for that?
>>
>> I.e.
>>
>> perf record -e cycles:uU would not set exclude_host not exclude_guest,
>> cycles:u excludes guest user, cycles:U excludes host user, would that be
>> possible?
>>
>> Anyway, I think that with what we have, your patch makes sense, having a
>> way to, without using 'perf kvm' still be able to sample the guest can
>> be done on top. of this.
>>
>> Xu, can we get your Reviewed-by if this addresses your concerns?

My concern is about do not break the perf kvm usages and Yao did it in v3.

Tested-by: Like Xu <like.xu@...ux.intel.com>

>>
>> - Arnaldo
> 
> Do you suggest we will create a new modifier 'U' as a follow-up patch?
> 
> cycles:u - Count host user space but it doesn't count the guest user space 
> (exclude_host = 0, exclude_guest = 1, exclude_kernel = 1, exclude_user = 0, 
> exclude_hv = 1)
> 
> cycles:U - Count the guest user space but it doesn't count the host user 
> space (exclude_host = 1, exclude_guest = 0, exclude_kernel = 1, 
> exclude_user = 0, exclude_hv = 1)
> 
> Is above understanding correct?

Do we really need to support sample guests without using perf kvm?

If it's true, I would prefer "cycles:uG" to cover guest user space
events only, "cycles:kG" to cover guest kernel space events only,
and only host events are sampled without the ":G" modifier by default.

I am not sure if ":G" has been used in perf.

At the very least, this v3 patch may not
block the follow-up patch from Yao (if any).

Thanks,
Like Xu

> 
> Thanks
> Jin Yao