linux-kernel - Re: [RFC PATCH] bpf: Add new bpf map type for timer

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Date:	Wed, 21 Oct 2015 18:38:26 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Ingo Molnar <mingo@...nel.org>, He Kuang <hekuang@...wei.com>
CC:	<ast@...nel.org>, <davem@...emloft.net>, <daniel@...earbox.net>,
	<rostedt@...dmis.org>, <xiakaixu@...wei.com>, <ast@...mgrid.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] bpf: Add new bpf map type for timer



On 2015/10/21 18:20, Ingo Molnar wrote:
> * He Kuang <hekuang@...wei.com> wrote:
>
>> ping and add ast@...mgrid.com, what's your opinion on this?
> Firstly, two days isn't nearly enough for a 'review timeout', secondly, have you
> seen the kbuild test reports?
>
> Thirdly, I suspect others will do a deeper review, but even stylistically the
> patch is a bit weird, for example these kinds of unstructured struct initializers
> are annoying:
>
>>>    struct bpf_map_def SEC("maps") timer_map = {
>>>    	.type = BPF_MAP_TYPE_TIMER_ARRAY,
>>>    	.key_size = sizeof(int),
>>>    	.value_size = sizeof(unsigned long long),
>>>    	.max_entries = 4,
>>>    };
>>>   	.map_alloc = fd_array_map_alloc,
>>>   	.map_free = fd_array_map_free,
>>>   	.map_get_next_key = array_map_get_next_key,
>>> -	.map_lookup_elem = fd_array_map_lookup_elem,
>>> +	.map_lookup_elem = empty_array_map_lookup_elem,
>>>   	.map_update_elem = fd_array_map_update_elem,
>>>   	.map_delete_elem = fd_array_map_delete_elem,
>>>   	.map_fd_get_ptr = prog_fd_array_get_ptr,
>>> @@ -312,7 +318,7 @@ static const struct bpf_map_ops perf_event_array_ops = {
>>>   	.map_alloc = fd_array_map_alloc,
>>>   	.map_free = perf_event_array_map_free,
>>>   	.map_get_next_key = array_map_get_next_key,
>>> -	.map_lookup_elem = fd_array_map_lookup_elem,
>>> +	.map_lookup_elem = empty_array_map_lookup_elem,
>>>   	.map_update_elem = fd_array_map_update_elem,
>>>   	.map_delete_elem = fd_array_map_delete_elem,
>>>   	.map_fd_get_ptr = perf_event_fd_array_get_ptr,
>>> +static const struct bpf_map_ops timer_array_ops = {
>>> +	.map_alloc = timer_array_map_alloc,
>>> +	.map_free = timer_array_map_free,
>>> +	.map_get_next_key = array_map_get_next_key,
>>> +	.map_lookup_elem = empty_array_map_lookup_elem,
>>> +	.map_update_elem = timer_array_map_update_elem,
>>> +	.map_delete_elem = timer_array_map_delete_elem,
>>> +};
>>> +
>>> +static struct bpf_map_type_list timer_array_type __read_mostly = {
>>> +	.ops = &timer_array_ops,
>>> +	.type = BPF_MAP_TYPE_TIMER_ARRAY,
>>> +};
> Please align initializations vertically, so the second column becomes readable,
> patterns in them become easy to see and individual entries become easier to
> compare.
>
> See for example kernel/sched/core.c:
>
> struct cgroup_subsys cpu_cgrp_subsys = {
>          .css_alloc      = cpu_cgroup_css_alloc,
>          .css_free       = cpu_cgroup_css_free,
>          .css_online     = cpu_cgroup_css_online,
>          .css_offline    = cpu_cgroup_css_offline,
>          .fork           = cpu_cgroup_fork,
>          .can_attach     = cpu_cgroup_can_attach,
>          .attach         = cpu_cgroup_attach,
>          .exit           = cpu_cgroup_exit,
>          .legacy_cftypes = cpu_files,
>          .early_init     = 1,
> };
>
> That's a _lot_ more readable than:
>
> struct cgroup_subsys cpu_cgrp_subsys = {
>          .css_alloc = cpu_cgroup_css_alloc,
>          .css_free = cpu_cgroup_css_free,
>          .css_online = cpu_cgroup_css_online,
>          .css_offline = cpu_cgroup_css_offline,
>          .fork = cpu_cgroup_fork,
>          .can_attach = cpu_cgroup_attach,

Here :)

>          .attach = cpu_cgroup_attach,
>          .exit = cpu_cgroup_exit,
>          .legacy_cftypes = cpu_files,
>          .early_init = 1,
> };
>
> right? For example I've hidden a small initialization bug into the second variant,
> how much time does it take for you to notice it?
>
> Thanks,
>
> 	Ingo


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