linux-kernel - Re: [PATCH] cxl/region: Support to calculate memory tier abstract distance

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Date: Wed, 5 Jun 2024 13:10:17 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Huang Ying <ying.huang@...el.com>
CC: Dan Williams <dan.j.williams@...el.com>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>,
	Dave Jiang <dave.jiang@...el.com>, Bharata B Rao <bharata@....com>, Alistair
 Popple <apopple@...dia.com>, "Aneesh Kumar K . V"
	<aneesh.kumar@...ux.ibm.com>
Subject: Re: [PATCH] cxl/region: Support to calculate memory tier abstract
 distance

On Fri, 31 May 2024 10:48:52 +0800
Huang Ying <ying.huang@...el.com> wrote:

> To place memory nodes backed by CXL regions in the appropriate memory
> tiers.  So that, pages can be promoted/demoted with the existing
> memory tiering mechanism.
> 
> The abstract distance is calculated based on the memory access latency
> and bandwidth of CXL regions.  Which in turn comes from the HMAT
> and CDAT, etc.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Cc: Dave Jiang <dave.jiang@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Bharata B Rao <bharata@....com>
> Cc: Alistair Popple <apopple@...dia.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>

Minor comments inline.  Otherwise, looks good to me.

Jonathan


> ---
>  drivers/cxl/core/region.c | 40 +++++++++++++++++++++++++++++++++++----
>  drivers/cxl/cxl.h         |  1 +
>  2 files changed, 37 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 00a9f0eef8dd..1f8f71a034ae 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -9,6 +9,7 @@
>  #include <linux/uuid.h>
>  #include <linux/sort.h>
>  #include <linux/idr.h>
> +#include <linux/memory-tiers.h>
>  #include <cxlmem.h>
>  #include <cxl.h>
>  #include "core.h"
> @@ -2304,14 +2305,20 @@ static bool cxl_region_update_coordinates(struct cxl_region *cxlr, int nid)
>  	return true;
>  }
>  
> +static int cxl_region_nid(struct cxl_region *cxlr)
> +{
> +	struct cxl_region_params *p = &cxlr->params;
> +	struct cxl_endpoint_decoder *cxled = p->targets[0];
> +	struct cxl_decoder *cxld = &cxled->cxld;
> +
> +	return phys_to_target_node(cxld->hpa_range.start);
> +}
> +
>  static int cxl_region_perf_attrs_callback(struct notifier_block *nb,
>  					  unsigned long action, void *arg)
>  {
>  	struct cxl_region *cxlr = container_of(nb, struct cxl_region,
>  					       memory_notifier);
> -	struct cxl_region_params *p = &cxlr->params;
> -	struct cxl_endpoint_decoder *cxled = p->targets[0];
> -	struct cxl_decoder *cxld = &cxled->cxld;
>  	struct memory_notify *mnb = arg;
>  	int nid = mnb->status_change_nid;
>  	int region_nid;
> @@ -2319,7 +2326,7 @@ static int cxl_region_perf_attrs_callback(struct notifier_block *nb,
>  	if (nid == NUMA_NO_NODE || action != MEM_ONLINE)
>  		return NOTIFY_DONE;
>  
> -	region_nid = phys_to_target_node(cxld->hpa_range.start);
> +	region_nid = cxl_region_nid(cxlr);
>  	if (nid != region_nid)
>  		return NOTIFY_DONE;
>  
> @@ -2329,6 +2336,27 @@ static int cxl_region_perf_attrs_callback(struct notifier_block *nb,
>  	return NOTIFY_OK;
>  }
>  
> +static int cxl_region_calculate_adistance(struct notifier_block *nb,
> +					  unsigned long nid, void *data)
> +{
> +	struct cxl_region *cxlr = container_of(nb, struct cxl_region,
> +					       adist_notifier);
> +	int region_nid;
> +	struct access_coordinate *perf;
> +	int *adist = data;
Local style looks to be reverse xmas tree subject to any dependencies etc.

> +
> +	region_nid = cxl_region_nid(cxlr);
> +	if (nid != region_nid)
> +		return NOTIFY_OK;
> +
> +	perf = &cxlr->coord[ACCESS_COORDINATE_CPU];
> +
> +	if (mt_perf_to_adistance(perf, adist))
> +		return NOTIFY_OK;
> +
> +	return NOTIFY_STOP;
> +}
> +
>  /**
>   * devm_cxl_add_region - Adds a region to a decoder
>   * @cxlrd: root decoder
> @@ -2380,6 +2408,10 @@ static struct cxl_region *devm_cxl_add_region(struct cxl_root_decoder *cxlrd,
>  	cxlr->memory_notifier.priority = CXL_CALLBACK_PRI;
>  	register_memory_notifier(&cxlr->memory_notifier);
>  
> +	cxlr->adist_notifier.notifier_call = cxl_region_calculate_adistance;
> +	cxlr->adist_notifier.priority = 100;
> +	register_mt_adistance_algorithm(&cxlr->adist_notifier);
> +
>  	rc = devm_add_action_or_reset(port->uport_dev, unregister_region, cxlr);
>  	if (rc)
>  		return ERR_PTR(rc);
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 603c0120cff8..6891f87f8ef7 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -534,6 +534,7 @@ struct cxl_region {
This has docs that need an updte.
>  	struct cxl_region_params params;
>  	struct access_coordinate coord[ACCESS_COORDINATE_MAX];
>  	struct notifier_block memory_notifier;
> +	struct notifier_block adist_notifier;
>  };
>  
>  struct cxl_nvdimm_bridge {