Re: [PATCH v2 3/6] perf tools: Show memory region in perf-c2c subcommand

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Arbitrary upper bound on UAPI memory region ID breaks forward compatibility for future memory tiering topologies.
--

--- Patch [3]: [PATCH v2 3/6] perf tools: Show memory region in perf-c2c subcommand ---
commit 06c5065732519d0c60d1739bb8a421f9120486b9
Author: Dapeng Mi <dapeng1.mi@linux.intel.com>

perf tools: Show memory region in perf-c2c subcommand

This commit adds a memory region field to the cacheline list view in
perf-c2c. The new field helps identify the memory region to which the
cacheline belongs.

Link: https://lore.kernel.org/all/20260114011750.350569-1-dapeng1.mi@linux.intel.com/

> diff --git a/tools/perf/builtin-c2c.c b/tools/perf/builtin-c2c.c
> index c9584dbedf77a..cba2e9f21ae7c 100644
> --- a/tools/perf/builtin-c2c.c
> +++ b/tools/perf/builtin-c2c.c

[ ... ]

> @@ -281,6 +282,18 @@ static void c2c_he__set_node(struct c2c_hist_entry *c2c_he,
>  	}
>  }
>  
> +static void c2c_he__set_mem_region(struct c2c_hist_entry *c2c_he,
> +				   unsigned int mem_region)
> +{
> +	if (WARN_ONCE(mem_region > PERF_MEM_REGION_MEM7,
> +		      "WARNING: invalid memory region ID\n"))
> +		return;

[Severity: Medium]
Does this arbitrary upper bound break forward compatibility for future memory
tiering topologies?

The UAPI field provides 5 bits, allowing for memory region IDs up to 31. By
rejecting regions greater than PERF_MEM_REGION_MEM7, valid region IDs from
future kernels or hardware architectures will be dropped and displayed as
"N/A", while also triggering a spurious warning.

It looks like the new display logic in dcacheline_node_mem_region() can
already mathematically scale to handle these higher values gracefully.

> +
> +	/* Update mem_region only if it really accesses memory */
> +	if (mem_region >= PERF_MEM_REGION_MMIO)
> +		c2c_he->mem_region = mem_region;
> +}
> +

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260714004359.179451-1-thomas.falcon@intel.com?part=3