linux-kernel - Re: [PATCH V3 01/13] perf/core, x86: Add PERF_SAMPLE_DATA_PAGE

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Date:   Thu, 31 Jan 2019 09:58:09 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     acme@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        linux-kernel@...r.kernel.org, eranian@...gle.com, jolsa@...hat.com,
        namhyung@...nel.org, ak@...ux.intel.com,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH V3 01/13] perf/core, x86: Add PERF_SAMPLE_DATA_PAGE_SIZE



On 1/31/2019 7:37 AM, Peter Zijlstra wrote:
> On Wed, Jan 30, 2019 at 06:23:42AM -0800, kan.liang@...ux.intel.com wrote:
>> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
>> index 374a197..03bf45d 100644
>> --- a/arch/x86/events/core.c
>> +++ b/arch/x86/events/core.c
>> @@ -2578,3 +2578,45 @@ void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap)
>>   	cap->events_mask_len	= x86_pmu.events_mask_len;
>>   }
>>   EXPORT_SYMBOL_GPL(perf_get_x86_pmu_capability);
>> +
>> +/*
>> + * map x86 page levels to perf page sizes
>> + */
>> +static const enum perf_page_size perf_page_size_map[PG_LEVEL_NUM] = {
>> +	[PG_LEVEL_NONE] = PERF_PAGE_SIZE_NONE,
>> +	[PG_LEVEL_4K]   = PERF_PAGE_SIZE_4K,
>> +	[PG_LEVEL_2M]   = PERF_PAGE_SIZE_2M,
>> +	[PG_LEVEL_1G]   = PERF_PAGE_SIZE_1G,
>> +	[PG_LEVEL_512G] = PERF_PAGE_SIZE_512G,
>> +};
>> +
>> +u64 perf_get_page_size(u64 virt)
>> +{
>> +	unsigned long flags;
>> +	unsigned int level;
>> +	pte_t *pte;
>> +
>> +	if (!virt)
>> +		return 0;
>> +
>> +	/*
>> +	 * Interrupts are disabled, so it prevents any tear down
>> +	 * of the page tables.
>> +	 * See the comment near struct mmu_table_batch.
>> +	 */
>> +	local_irq_save(flags);
>> +	if (virt >= TASK_SIZE)
>> +		pte = lookup_address(virt, &level);
>> +	else {
>> +		if (current->mm)
>> +			pte = lookup_address_in_pgd(pgd_offset(current->mm, virt),
>> +						    virt, &level);
> 
> Aside from all the missin {}, I'm fairly sure this is broken since this
> happens from NMI context. This can interrupt switch_mm() and things like
> use_temporary_mm().
> 
> Also; why does this live in the x86 code and not in the generic code?
>

This is x86 implementation.
In generic code, there is a __weak function. I'll make it clear in the 
change log in v4.

+/* Return page size of given virtual address. IRQ-safe required. */
+u64 __weak perf_get_page_size(u64 virt)
+{
+	return PERF_PAGE_SIZE_NONE;
+}


>> +		else
>> +			level = PG_LEVEL_NUM;
>> +	}
>> +	local_irq_restore(flags);
>> +	if (level >= PG_LEVEL_NUM)
>> +		return PERF_PAGE_SIZE_NONE;
>> +
>> +	return (u64)perf_page_size_map[level];
>> +}
> 
>> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
>> index 7198ddd..79daacd 100644
>> --- a/include/uapi/linux/perf_event.h
>> +++ b/include/uapi/linux/perf_event.h
>> @@ -141,8 +141,9 @@ enum perf_event_sample_format {
>>   	PERF_SAMPLE_TRANSACTION			= 1U << 17,
>>   	PERF_SAMPLE_REGS_INTR			= 1U << 18,
>>   	PERF_SAMPLE_PHYS_ADDR			= 1U << 19,
>> +	PERF_SAMPLE_DATA_PAGE_SIZE		= 1U << 20,
>>   
>> -	PERF_SAMPLE_MAX = 1U << 20,		/* non-ABI */
>> +	PERF_SAMPLE_MAX = 1U << 21,		/* non-ABI */
>>   
>>   	__PERF_SAMPLE_CALLCHAIN_EARLY		= 1ULL << 63, /* non-ABI; internal use */
>>   };
>> @@ -863,6 +864,7 @@ enum perf_event_type {
>>   	 *	{ u64			abi; # enum perf_sample_regs_abi
>>   	 *	  u64			regs[weight(mask)]; } && PERF_SAMPLE_REGS_INTR
>>   	 *	{ u64			phys_addr;} && PERF_SAMPLE_PHYS_ADDR
>> +	 *	{ u64			data_page_size;} && PERF_SAMPLE_DATA_PAGE_SIZE
>>   	 * };
>>   	 */
>>   	PERF_RECORD_SAMPLE			= 9,
>> @@ -1150,6 +1152,18 @@ union perf_mem_data_src {
>>   #define PERF_MEM_S(a, s) \
>>   	(((__u64)PERF_MEM_##a##_##s) << PERF_MEM_##a##_SHIFT)
>>   
>> +
>> +enum perf_page_size {
>> +	PERF_PAGE_SIZE_NONE,
>> +	PERF_PAGE_SIZE_4K,
>> +	PERF_PAGE_SIZE_8K,
>> +	PERF_PAGE_SIZE_16K,
>> +	PERF_PAGE_SIZE_64K,
>> +	PERF_PAGE_SIZE_2M,
>> +	PERF_PAGE_SIZE_1G,
>> +	PERF_PAGE_SIZE_512G,
>> +};
> 
> Since you have a u64 to store this in, WTH do you use this limited enum?
> Are you very sure this covers all the possible page sizes for all
> architectures?
> 
> Why not simply report the page size in bytes?
> 

I will use the page size instead in V4.

Thanks,
Kan