linux-kernel - Re: [PATCH V4 01/13] perf/core, x86: Add PERF_SAMPLE_DATA_PAGE

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Date:   Fri, 1 Feb 2019 09:45:59 -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, luto@...capital.net,
        Vlastimil Babka <vbabka@...e.cz>, kirill@...temov.name
Subject: Re: [PATCH V4 01/13] perf/core, x86: Add PERF_SAMPLE_DATA_PAGE_SIZE



On 2/1/2019 4:22 AM, Peter Zijlstra wrote:
> On Thu, Jan 31, 2019 at 12:27:54PM -0800, kan.liang@...ux.intel.com wrote:
>> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
>> index 374a197..229a73b 100644
>> --- a/arch/x86/events/core.c
>> +++ b/arch/x86/events/core.c
>> @@ -2578,3 +2578,34 @@ 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);
>> +
>> +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);
>> +		} else
>> +			level = PG_LEVEL_NUM;
>> +	}
>> +	local_irq_restore(flags);
>> +	if (level >= PG_LEVEL_NUM)
>> +		return 0;
>> +
>> +	return (u64)page_level_size(level);
>> +}
> 
> *sigh* there really isn't anything x86 specific there.

OK. I will split the patch and move the common code to a dedicated patch 
in V5. I will try the proposed code and do some tests on X86.

> >> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index 236bb8d..d233f45 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -6352,6 +6358,12 @@ static u64 perf_virt_to_phys(u64 virt)
>>   	return phys_addr;
>>   }
>>   
>> +/* Return page size of given virtual address. IRQ-safe required. */
>> +u64 __weak perf_get_page_size(u64 virt)
>> +{
>> +	return 0;
>> +}
>> +
>>   static struct perf_callchain_entry __empty_callchain = { .nr = 0, };
>>   
>>   struct perf_callchain_entry *
> 
> How about something like so instead?
> 
> (completely untested, will likely make your grandma eat puppies
That's not funny!


Kan