linux-kernel - Re: [PATCH v4 RESEND 3/5] perf/x86/lbr: Move cpuc->lbr

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Date:   Wed, 24 Mar 2021 13:42:24 +0800
From:   Like Xu <like.xu@...ux.intel.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Kan Liang <kan.liang@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 RESEND 3/5] perf/x86/lbr: Move cpuc->lbr_xsave
 allocation out of sleeping region

On 2021/3/24 12:04, Namhyung Kim wrote:
> On Wed, Mar 24, 2021 at 12:47 PM Like Xu <like.xu@...ux.intel.com> wrote:
>>
>> Hi Namhyung,
>>
>> On 2021/3/24 9:32, Namhyung Kim wrote:
>>> Hello,
>>>
>>> On Mon, Mar 22, 2021 at 3:14 PM Like Xu <like.xu@...ux.intel.com> wrote:
>>>> +void reserve_lbr_buffers(struct perf_event *event)
>>>> +{
>>>> +       struct kmem_cache *kmem_cache = x86_get_pmu()->task_ctx_cache;
>>>> +       struct cpu_hw_events *cpuc;
>>>> +       int cpu;
>>>> +
>>>> +       if (!static_cpu_has(X86_FEATURE_ARCH_LBR))
>>>> +               return;
>>>> +
>>>> +       for_each_possible_cpu(cpu) {
>>>> +               cpuc = per_cpu_ptr(&cpu_hw_events, cpu);
>>>> +               if (kmem_cache && !cpuc->lbr_xsave && !event->attr.precise_ip)
>>>> +                       cpuc->lbr_xsave = kmem_cache_alloc(kmem_cache, GFP_KERNEL);
>>>> +       }
>>>> +}
>>>
>>> I think we should use kmem_cache_alloc_node().
>>
>> "kmem_cache_alloc_node - Allocate an object on the specified node"
>>
>> The reserve_lbr_buffers() is called in __x86_pmu_event_init().
>> When the LBR perf_event is scheduled to another node, it seems
>> that we will not call init() and allocate again.
>>
>> Do you mean use kmem_cache_alloc_node() for each numa_nodes_parsed ?
> 
> I assume cpuc->lbr_xsave will be accessed for that cpu only.
> Then it needs to allocate it in the node that cpu belongs to.
> Something like below..
> 
>      cpuc->lbr_xsave = kmem_cache_alloc_node(kmem_cache, GFP_KERNEL,
>                                                 cpu_to_node(cpu));

Thanks, it helps and I will apply it in the next version.

> 
> Thanks,
> Namhyung
>