linux-kernel - Re: [PATCH 05/26] cxl/core: Simplify cxl_dpa_set

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Date: Tue, 26 Mar 2024 10:46:58 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Ira Weiny <ira.weiny@...el.com>, Fan Ni <fan.ni@...sung.com>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Navneet Singh <navneet.singh@...el.com>
Cc: Dan Williams <dan.j.williams@...el.com>,
 Davidlohr Bueso <dave@...olabs.net>,
 Alison Schofield <alison.schofield@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, linux-btrfs@...r.kernel.org,
 linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/26] cxl/core: Simplify cxl_dpa_set_mode()



On 3/24/24 4:18 PM, Ira Weiny wrote:
> cxl_dpa_set_mode() checks the mode for validity two times, once outside
> of the DPA RW semaphore and again within.  The function is not in a
> critical path.  Prior to Dynamic Capacity the extra check was not much
> of an issue.  The addition of DC modes increases the complexity of
> the check.
> 
> Simplify the mode check before adding the more complex DC modes.

I would augment this by saying simplify "by using scope-based resource menagement".
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> 
> ---
> Changes for v1:
> [iweiny: new patch]
> [Jonathan: based on getting rid of the loop in cxl_dpa_set_mode]
> [Jonathan: standardize on resource_size() == 0]
> ---
>  drivers/cxl/core/hdm.c | 45 ++++++++++++++++++---------------------------
>  1 file changed, 18 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 7d97790b893d..66b8419fd0c3 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -411,44 +411,35 @@ int cxl_dpa_set_mode(struct cxl_endpoint_decoder *cxled,
>  	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
>  	struct cxl_dev_state *cxlds = cxlmd->cxlds;
>  	struct device *dev = &cxled->cxld.dev;
> -	int rc;
>  
> +	guard(rwsem_write)(&cxl_dpa_rwsem);
> +	if (cxled->cxld.flags & CXL_DECODER_F_ENABLE)
> +		return -EBUSY;
> +
> +	/*
> +	 * Check that the mode is supported by the current partition
> +	 * configuration
> +	 */
>  	switch (mode) {
>  	case CXL_DECODER_RAM:
> +		if (!resource_size(&cxlds->ram_res)) {
> +			dev_dbg(dev, "no available ram capacity\n");
> +			return -ENXIO;
> +		}
> +		break;
>  	case CXL_DECODER_PMEM:
> +		if (!resource_size(&cxlds->pmem_res)) {
> +			dev_dbg(dev, "no available pmem capacity\n");
> +			return -ENXIO;
> +		}
>  		break;
>  	default:
>  		dev_dbg(dev, "unsupported mode: %d\n", mode);
>  		return -EINVAL;
>  	}
>  
> -	down_write(&cxl_dpa_rwsem);
> -	if (cxled->cxld.flags & CXL_DECODER_F_ENABLE) {
> -		rc = -EBUSY;
> -		goto out;
> -	}
> -
> -	/*
> -	 * Only allow modes that are supported by the current partition
> -	 * configuration
> -	 */
> -	if (mode == CXL_DECODER_PMEM && !resource_size(&cxlds->pmem_res)) {
> -		dev_dbg(dev, "no available pmem capacity\n");
> -		rc = -ENXIO;
> -		goto out;
> -	}
> -	if (mode == CXL_DECODER_RAM && !resource_size(&cxlds->ram_res)) {
> -		dev_dbg(dev, "no available ram capacity\n");
> -		rc = -ENXIO;
> -		goto out;
> -	}
> -
>  	cxled->mode = mode;
> -	rc = 0;
> -out:
> -	up_write(&cxl_dpa_rwsem);
> -
> -	return rc;
> +	return 0;
>  }
>  
>  int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
>