Re: [PATCH v5 10/10] x86/resctrl: Enable read L3 occupancy via MMIO

[Reinette Chatre]

Hi Chenyu,

On 7/1/26 6:47 AM, Chen Yu wrote:
> Implement the erdt_mon_read().
> 
> Use the CMRC (Cache Monitoring Registers for CPU Agents Description)
> ACPI sub-table to read LLC occupancy counters for each RMID via MMIO
> when ERDT is enabled. This CMRC information is stored in the
> rdt_hw_l3_mon_domain, which could be accessed directly.
> 
> Suggested-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> ---
> v4->v5:
>    Split into a smaller patch; no functional code changes in the low level
>    implementation, but read from the CMRC information stored per domain .
> ---
>  arch/x86/kernel/cpu/resctrl/erdt.c | 63 ++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/erdt.c b/arch/x86/kernel/cpu/resctrl/erdt.c
> index 1114ad4e3b42..f897c7e247bb 100644
> --- a/arch/x86/kernel/cpu/resctrl/erdt.c
> +++ b/arch/x86/kernel/cpu/resctrl/erdt.c
> @@ -36,6 +36,9 @@ static u32 valid_subtbl_mask;
>  
>  bool erdt_support_features(int flag)
>  {
> +	if (flag == X86_FEATURE_CQM_OCCUP_LLC)
> +		return valid_subtbl_mask & BIT(ACPI_ERDT_TYPE_CMRC);
> +
>  	return false;
>  }
>  
> @@ -57,8 +60,68 @@ int erdt_get_max_rmid(int cpu)
>  	return -1;
>  }
>  
> +static void __iomem *cmrc_index_function_1(struct erdt_domain_info *d,
> +					   struct acpi_erdt_cmrc *cmrc, int rmid)
> +{
> +	u16 clump_size, stride_size;
> +	void __iomem *vaddr;
> +
> +	clump_size = cmrc->clump_size;
> +	stride_size = cmrc->clump_stride;
> +
> +	/*
> +	 * MMIO_ADDRESS_for_RMID# = CMRC Base +
> +	 *   (RMID / ClumpSize) * Stride +
> +	 *   (RMID % ClumpSize) * 8
> +	 */
> +	vaddr = d->base[ERDT_MMIO_CMRC_BASE] +
> +		(rmid / clump_size) * stride_size +
> +		(rmid % clump_size) * 8;
> +
> +	return vaddr;
> +}
> +
> +static int erdt_read_l3_occupancy(struct erdt_domain_info *d, int rmid, u64 *val)
> +{
> +	struct acpi_erdt_cmrc *cmrc;
> +	void __iomem *vaddr;
> +	u64 l3_cmt_count;
> +	u32 offset;
> +
> +	cmrc = d->cmrc;
> +	if (!cmrc)
> +		return -EIO;
> +
> +	offset = (rmid / cmrc->clump_size) * cmrc->clump_stride +
> +		 (rmid % cmrc->clump_size) * 8;

This is the same function open coded in cmrc_index_function_1() - can it just be coded once
and then re-used?

> +	/* Overflow of cmt_reg_size * SZ_4K already validated in erdt_ioremap(). */
> +	if (offset + sizeof(u64) > (u32)cmrc->cmt_reg_size * SZ_4K)
> +		return -EINVAL;
> +
> +	vaddr = cmrc_index_function_1(d, cmrc, rmid);
> +
> +	l3_cmt_count = readq(vaddr);
> +	if (l3_cmt_count & UNAVAILABLE_COUNTER)
> +		return -EINVAL;
> +
> +	*val = l3_cmt_count * cmrc->up_scale;
> +
> +	return 0;
> +}
> +
Reinette