linux-kernel - Re: [PATCH 1/4] coresight: tmc-etr: Do not call smp_processor

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Date:   Thu, 30 May 2019 16:52:40 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     robin.murphy@....com, mathieu.poirier@...aro.org
Cc:     coresight@...ts.linaro.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/4] coresight: tmc-etr: Do not call smp_processor_id()
 from preemptible

Hi Robin,

On 10/05/2019 11:38, Robin Murphy wrote:
> Hi Suzuki,
> 
> On 10/05/2019 10:31, Suzuki K Poulose wrote:
>> Instead of using smp_processor_id() to figure out the node,
>> use the numa_node_id() for the current CPU node to avoid
>> splats like :


>
>> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
>> index 793639f..cae9d8a 100644
>> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
>> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
>> @@ -1323,13 +1323,11 @@ static struct etr_perf_buffer *
>>    tmc_etr_setup_perf_buf(struct tmc_drvdata *drvdata, struct perf_event *event,
>>    		       int nr_pages, void **pages, bool snapshot)
>>    {
>> -	int node, cpu = event->cpu;
>> +	int node;
>>    	struct etr_buf *etr_buf;
>>    	struct etr_perf_buffer *etr_perf;
>>    
>> -	if (cpu == -1)
>> -		cpu = smp_processor_id();
>> -	node = cpu_to_node(cpu);
>> +	node = (event->cpu == -1) ? numa_node_id() : cpu_to_node(event->cpu);
> 
> If cpu == -1 represents a "don't care" scenario, it might be clearer to
> just use NUMA_NO_NODE instead, and let the allocator handle it.

Thanks for the suggestion, will use that instead

Cheers
Suzuki