linux-kernel - Re: [PATCH v4 3/3] acpi,srat: give memory block size advice based on CFMWS alignment

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Message-ID: <c47337ea-f20e-44eb-95e8-c29b2db849a7@redhat.com>
Date: Wed, 30 Oct 2024 11:40:08 +0100
From: David Hildenbrand <david@...hat.com>
To: Gregory Price <gourry@...rry.net>, x86@...nel.org,
 linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org, linux-mm@...ck.org
Cc: linux-cxl@...r.kernel.org, Jonathan.Cameron@...wei.com,
 dan.j.williams@...el.com, rrichter@....com, Terry.Bowman@....com,
 dave.jiang@...el.com, ira.weiny@...el.com, alison.schofield@...el.com,
 dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
 rafael@...nel.org, lenb@...nel.org, osalvador@...e.de,
 gregkh@...uxfoundation.org, akpm@...ux-foundation.org, rppt@...nel.org
Subject: Re: [PATCH v4 3/3] acpi,srat: give memory block size advice based on
 CFMWS alignment

On 29.10.24 21:20, Gregory Price wrote:
> Capacity is stranded when CFMWS regions are not aligned to block size.
> On x86, block size increases with capacity (2G blocks @ 64G capacity).
> 
> Use CFMWS base/size to report memory block size alignment advice.
> 
> Suggested-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Gregory Price <gourry@...rry.net>
> ---
>   drivers/acpi/numa/srat.c | 19 +++++++++++++++++--
>   1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
> index 44f91f2c6c5d..a24aff38c465 100644
> --- a/drivers/acpi/numa/srat.c
> +++ b/drivers/acpi/numa/srat.c
> @@ -14,6 +14,7 @@
>   #include <linux/errno.h>
>   #include <linux/acpi.h>
>   #include <linux/memblock.h>
> +#include <linux/memory.h>
>   #include <linux/numa.h>
>   #include <linux/nodemask.h>
>   #include <linux/topology.h>
> @@ -338,12 +339,26 @@ static int __init acpi_parse_cfmws(union acpi_subtable_headers *header,
>   {
>   	struct acpi_cedt_cfmws *cfmws;
>   	int *fake_pxm = arg;
> -	u64 start, end;
> +	u64 start, end, align, size;
>   	int node;
>   
>   	cfmws = (struct acpi_cedt_cfmws *)header;
>   	start = cfmws->base_hpa;
> -	end = cfmws->base_hpa + cfmws->window_size;
> +	size = cfmws->window_size;
> +	end = cfmws->base_hpa + size;
> +
> +	/* Align memblock size to CFMW regions if possible */
> +	for (align = SZ_64T; align >= SZ_256M; align >>= 1) {
> +		if (IS_ALIGNED(start, align) && IS_ALIGNED(size, align))
> +			break;
> +	}

Are there maybe some nice tricks bi-tricks to avoid the loop and these 
hardcoded limits? :)

align = 1UL << __ffs(start | end));

Assuming "unsigned long" is sufficient in this code (64bit) and "start | 
end" will never be 0.

-- 
Cheers,

David / dhildenb