linux-kernel - Re: [PATCH 3/8] perf/arm-cmn: Ensure dtm

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Message-ID: <Zr8ma7pt7te0qxNG@J2N7QTR9R3>
Date: Fri, 16 Aug 2024 11:14:03 +0100
From: Mark Rutland <mark.rutland@....com>
To: Robin Murphy <robin.murphy@....com>
Cc: will@...nel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, ilkka@...amperecomputing.com
Subject: Re: [PATCH 3/8] perf/arm-cmn: Ensure dtm_idx is big enough

On Fri, Aug 09, 2024 at 08:15:42PM +0100, Robin Murphy wrote:
> While CMN_MAX_DIMENSION was bumped to 12 for CMN-650, that only supports
> up to a 10x10 mesh, so bumping dtm_idx to 256 bits at the time worked
> out OK in practice. However CMN-700 did finally support up to 144 XPs,
> and thus needs a worst-case 288 bits of dtm_idx for an aggregated XP
> event on a maxed-out config. Oops.
> 
> Fixes: 23760a014417 ("perf/arm-cmn: Add CMN-700 support")
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
>  drivers/perf/arm-cmn.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index 0e2e12e2f4fb..c9a2b21a7aec 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -563,7 +563,7 @@ static void arm_cmn_debugfs_init(struct arm_cmn *cmn, int id) {}
>  
>  struct arm_cmn_hw_event {
>  	struct arm_cmn_node *dn;
> -	u64 dtm_idx[4];
> +	u64 dtm_idx[5];

Can't we size this based on CMN_MAX_DIMENSION (or CMN_MAX_XPS or
CMN_MAX_DTMS), to make that clear?

>From the desciription in the commit message it sounds like you need 2 *
CMN_MAX_XPS bits, i.e.

	#define DTM_IDX_BITS	(2 * CMN_MAX_XPS)

	u64 dtm_idx[DIV_ROUND_UP(DTM_IDX_BITS, 64)];

Mark.

>  	s8 dtc_idx[CMN_MAX_DTCS];
>  	u8 num_dns;
>  	u8 dtm_offset;
> -- 
> 2.39.2.101.g768bb238c484.dirty
>