Subject: Re: [PATCH 8/8][v4] powerpc/perf: Export Power7 memory hierarchy info to user space.

From: Anshuman Khandual <[email-masked]>
Date: Thu, 19 Sep 2013 14:11:22 +0530

On 09/14/2013 06:19 AM, Sukadev Bhattiprolu wrote:
> +static void power7_get_mem_data_src(union perf_mem_data_src *dsrc,
> +			struct pt_regs *regs)
> +{
> +	u64 idx;
> +	u64 mmcra = regs->dsisr;
> +	u64 addr;
> +	int ret;
> +	unsigned int instr;
> +
> +	if (mmcra & POWER7_MMCRA_DCACHE_MISS) {
> +		idx = mmcra & POWER7_MMCRA_DCACHE_SRC_MASK;
> +		idx >>= POWER7_MMCRA_DCACHE_SRC_SHIFT;
> +
> +		dsrc->val |= dcache_src_map[idx];
> +		return;
> +	}
> +
> +	instr = 0;
> +	addr = perf_instruction_pointer(regs);
> +
> +	if (is_kernel_addr(addr))
> +		instr = *(unsigned int *)addr;
> +	else {
> +		pagefault_disable();
> +		ret = __get_user_inatomic(instr, (unsigned int __user *)addr);
> +		pagefault_enable();
> +		if (ret)
> +			instr = 0;
> +	}
> +	if (instr && instr_is_load_store(&instr))

Wondering if there is any possibility of getting positive values for
"(mmcra & POWER7_MMCRA_DCACHE_SRC_MASK) >> POWER7_MMCRA_DCACHE_SRC_SHIFT"
when the marked instruction did not have MMCRA[POWER7_MMCRA_DCACHE_MISS]
bit set. In that case we should actually compute dsrc->val as in the previous
case. I did couple of experiments on a P7 box, but was not able to find a
instance for a marked instruction whose MMCRA[POWER7_MMCRA_DCACHE_MISS] bit
not set and have a positive value POWER7_MMCRA_DCACHE_SRC field.