RE: [NDCTL PATCH v5 3/4] ndctl: cxl: add QoS class check for CXL region creation

[Wonjae Lee]

On Thu, Feb 01, 2024 at 04:05:06PM -0700, Dave Jiang wrote:
> The CFMWS provides a QTG ID. The kernel driver creates a root decoder that
> represents the CFMWS. A qos_class attribute is exported via sysfs for the root
> decoder.
>
> One or more QoS class tokens are retrieved via QTG ID _DSM from the ACPI0017
> device for a CXL memory device. The input for the _DSM is the read and write
> latency and bandwidth for the path between the device and the CPU. The
> numbers are constructed by the kernel driver for the _DSM input. When a
> device is probed, QoS class tokens  are retrieved. This is useful for a
> hot-plugged CXL memory device that does not have regions created.
>
> Add a QoS check during region creation. Emit a warning if the qos_class
> token from the root decoder is different than the mem device qos_class
> token. User parameter options are provided to fail instead of just
> warning.
>
> Reviewed-by: Alison Schofield <alison.schofi...@intel.com>
> Signed-off-by: Dave Jiang <dave.ji...@intel.com>
> ---
>  Documentation/cxl/cxl-create-region.txt |  9 ++++
>  cxl/region.c                            | 56 ++++++++++++++++++++++++-
>  2 files changed, 64 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/cxl/cxl-create-region.txt 
> b/Documentation/cxl/cxl-create-region.txt
> index f11a412bddfe..d5e34cf38236 100644
> --- a/Documentation/cxl/cxl-create-region.txt
> +++ b/Documentation/cxl/cxl-create-region.txt
> @@ -105,6 +105,15 @@ include::bus-option.txt[]
>   supplied, the first cross-host bridge (if available), decoder that
>   supports the largest interleave will be chosen.
>
> +-e::
> +--strict::
> + Enforce strict execution where any potential error will force failure.
> + For example, if qos_class mismatches region creation will fail.
> +
> +-q::
> +--no-enforce-qos::
> + Parameter to bypass qos_class mismatch failure. Will only emit warning.
> +
>  include::human-option.txt[]
>
>  include::debug-option.txt[]
> diff --git a/cxl/region.c b/cxl/region.c
> index 3a762db4800e..f9033fa0afbf 100644
> --- a/cxl/region.c
> +++ b/cxl/region.c
> @@ -32,6 +32,8 @@ static struct region_params {
>   bool force;
>   bool human;
>   bool debug;
> + bool strict;
> + bool no_qos;
>  } param = {
>   .ways = INT_MAX,
>   .granularity = INT_MAX,
> @@ -49,6 +51,8 @@ struct parsed_params {
>   const char **argv;
>   struct cxl_decoder *root_decoder;
>   enum cxl_decoder_mode mode;
> + bool strict;
> + bool no_qos;
>  };
>
>  enum region_actions {
> @@ -81,7 +85,9 @@ OPT_STRING('U', "uuid", &param.uuid, \
>      "region uuid", "uuid for the new region (default: autogenerate)"), \
>  OPT_BOOLEAN('m', "memdevs", &param.memdevs, \
>       "non-option arguments are memdevs"), \
> -OPT_BOOLEAN('u', "human", &param.human, "use human friendly number formats")
> +OPT_BOOLEAN('u', "human", &param.human, "use human friendly number 
> formats"), \
> +OPT_BOOLEAN('e', "strict", &param.strict, "strict execution enforcement"), \
> +OPT_BOOLEAN('q', "no-enforce-qos", &param.no_qos, "no enforce of qos_class")
>
>  static const struct option create_options[] = {
>   BASE_OPTIONS(),
> @@ -360,6 +366,9 @@ static int parse_create_options(struct cxl_ctx *ctx, int 
> count,
>       }
>   }
>
> + p->strict = param.strict;
> + p->no_qos = param.no_qos;
> +
>   return 0;
>
>  err:
> @@ -467,6 +476,49 @@ static void set_type_from_decoder(struct cxl_ctx *ctx, 
> struct parsed_params *p)
>       p->mode = CXL_DECODER_MODE_PMEM;
>  }
>
> +static int create_region_validate_qos_class(struct cxl_ctx *ctx,
> +                     struct parsed_params *p)
> +{
> + int root_qos_class;
> + int qos_class;
> + int i;
> +
> + root_qos_class = cxl_root_decoder_get_qos_class(p->root_decoder);
> + if (root_qos_class == CXL_QOS_CLASS_NONE)
> +     return 0;
> +
> + for (i = 0; i < p->ways; i++) {
> +     struct json_object *jobj =
> +         json_object_array_get_idx(p->memdevs, i);
> +     struct cxl_memdev *memdev = json_object_get_userdata(jobj);
> +
> +     if (p->mode == CXL_DECODER_MODE_RAM)
> +         qos_class = cxl_memdev_get_ram_qos_class(memdev);
> +     else
> +         qos_class = cxl_memdev_get_pmem_qos_class(memdev);
> +
> +     /* No qos_class entries. Possibly no kernel support */
> +     if (qos_class == CXL_QOS_CLASS_NONE)
> +         break;
> +
> +     if (qos_class != root_qos_class) {
> +         if (p->strict && !p->no_qos) {
> +             log_err(&rl, "%s QoS Class mismatches %s\n",
> +                 cxl_decoder_get_devname(p->root_decoder),
> +                 cxl_memdev_get_devname(memdev));
> +
> +             return -ENXIO;
> +         }
> +
> +         log_notice(&rl, "%s QoS Class mismatches %s\n",
> +                cxl_decoder_get_devname(p->root_decoder),
> +                cxl_memdev_get_devname(memdev));
> +     }
> + }
> +
> + return 0;
> +}
> +
>  static int create_region_validate_config(struct cxl_ctx *ctx,
>                    struct parsed_params *p)
>  {
> @@ -507,6 +559,8 @@ found:
>       return rc;
>
>   collect_minsize(ctx, p);
> + create_region_validate_qos_class(ctx, p);

Hello,

IIUC, if the strict option is given and a qos class mismatch occurs,
the region creation should fail. To do that, shouldn't the return
value of create_region_validate_qos_class() be handled like below?

diff --git a/cxl/region.c b/cxl/region.c
index f9033fa..0468f5f 100644
--- a/cxl/region.c
+++ b/cxl/region.c
@@ -559,7 +559,9 @@ found:
                return rc;

        collect_minsize(ctx, p);
-       create_region_validate_qos_class(ctx, p);
+       rc = create_region_validate_qos_class(ctx, p);
+       if (rc)
+               return rc;

        return 0;
 }

Thanks,
Wonjae