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Date: Wed, 12 Jun 2024 10:09:14 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Alison Schofield <alison.schofield@...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>, Jonathan Cameron
<Jonathan.Cameron@...wei.com>, 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 -V2] cxl/region: Support to calculate memory tier
abstract distance
Hi, Alison,
Thanks for review!
Alison Schofield <alison.schofield@...el.com> writes:
> On Tue, Jun 11, 2024 at 01:54:23PM +0800, Ying Huang 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.
>
> How about more context for the unfamiliar because my first lookup was
> what's an 'abstract distance'? (not sure I even got it right below ;))
Sorry about this.
> An abstract distance value must be assigned by the driver that makes
> the memory available to the system. It reflects relative performance
> and is used to place memory nodes backed by CXL regions in the appropriate
> memory tiers allowing promotion/demotion within the existing memory tiering
> mechanism.
This looks good. Will use it. Thanks!
>>
>> 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.
>
> etc ?
> I think the latency and bandwidth were already calculated, so you
> don't need to explain those. Perhaps drop the whole 'While in turn
> come from..." part.
Sure.
> a bit below...
>
>>
>> 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>
>> ---
>> Changes:
>>
>> v2:
>>
>> - Added comments to struct cxl_region and minor fixes (Thanks Jonathan!)
>> - Link to v1: https://lore.kernel.org/linux-cxl/20240531024852.282767-1-ying.huang@intel.com/
>>
>> ---
>> drivers/cxl/core/region.c | 40 +++++++++++++++++++++++++++++++++++----
>> drivers/cxl/cxl.h | 2 ++
>> 2 files changed, 38 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index 3c2b6144be23..81d0910c0a02 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);
>> +}
>> +
>
> I believe it's OK to send a resource_size_t to phys_to_target_node()
> like this:
>
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -2308,10 +2308,8 @@ static bool cxl_region_update_coordinates(struct cxl_region *cxlr, int nid)
> 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);
> + return phys_to_target_node(p->res->start);
> }
>
I believe this works. But the original implementation is just a
mechanical code movement from cxl_region_perf_attrs_callback(). So, I
prefer to keep it stupid. Then, further optimization can be done on top
of it. Is it good for you?
>
>> 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);
>> + struct access_coordinate *perf;
>> + int *adist = data;
>> + int region_nid;
>> +
>> + 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
>> @@ -2371,6 +2399,10 @@ 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..f46252373159 100644
>> --- a/drivers/cxl/cxl.h
>> +++ b/drivers/cxl/cxl.h
>> @@ -522,6 +522,7 @@ struct cxl_region_params {
>> * @params: active + config params for the region
>> * @coord: QoS access coordinates for the region
>> * @memory_notifier: notifier for setting the access coordinates to node
>> + * @adist_notifier: notifier for calculating the abstract distance of node
>> */
>> struct cxl_region {
>> struct device dev;
>> @@ -534,6 +535,7 @@ struct cxl_region {
>> 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 {
>> --
>> 2.39.2
>>
>>
--
Best Regards,
Huang, Ying
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