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Subject: Re: [PATCH v4 RESEND 3/5] perf/x86/lbr: Move cpuc->lbr_xsave
 allocation out of sleeping region
To:     Namhyung Kim <namhyung@kernel.org>,
        Kan Liang <kan.liang@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>, x86@kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>
References: <20210322060635.821531-1-like.xu@linux.intel.com>
 <20210322060635.821531-4-like.xu@linux.intel.com>
 <CAM9d7ci7qj47xDC3z2AzYGjnFdPRNsuEPGivZ1_re-XGhoBwMg@mail.gmail.com>
From:   Like Xu <like.xu@linux.intel.com>
Organization: Intel OTC
Message-ID: <5fda3599-1b51-5f58-fdcc-2afcf6d4968b@linux.intel.com>
Date:   Wed, 24 Mar 2021 11:46:52 +0800
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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@linux.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 ?

> 
> Thanks,
> Namhyung
>