linux-kernel - Re: [PATCH v3 3/3] samples/bpf: example of get selected PMU counter value

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Date:	Fri, 24 Jul 2015 09:54:01 +0800
From:	xiakaixu <xiakaixu@...wei.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
CC:	<davem@...emloft.net>, <acme@...nel.org>, <mingo@...hat.com>,
	<a.p.zijlstra@...llo.nl>, <masami.hiramatsu.pt@...achi.com>,
	<jolsa@...nel.org>, <wangnan0@...wei.com>,
	<linux-kernel@...r.kernel.org>, <pi3orama@....com>,
	<hekuang@...wei.com>
Subject: Re: [PATCH v3 3/3] samples/bpf: example of get selected PMU counter
 value

于 2015/7/24 6:59, Alexei Starovoitov 写道:
> On 7/23/15 2:42 AM, Kaixu Xia wrote:
>> This is a simple example and shows how to use the new ability
>> to get the selected Hardware PMU counter value.
>>
>> Signed-off-by: Kaixu Xia <xiakaixu@...wei.com>
> ...
>> +struct bpf_map_def SEC("maps") my_map = {
>> +    .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
>> +    .key_size = sizeof(int),
>> +    .value_size = sizeof(unsigned long),
>> +    .max_entries = 32,
>> +};
> 
> wait. how did it work here? value_size should be u32.

I tested the whole thing on ARM board. You are ringt, it
should be u32.
When create the array map, we choose the array->elem_size as
round_up(attr->value_size, 8), why 8?

Thanks!
> 
> 
> 


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