linux-kernel - Re: [PATCH] xen: make multicall debug boot time selectable

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Message-ID: <d28f8da5-7903-41c8-9213-4e24e376c837@oracle.com>
Date: Fri, 5 Jul 2024 18:36:10 -0400
From: boris.ostrovsky@...cle.com
To: Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-doc@...r.kernel.org
Cc: Jonathan Corbet <corbet@....net>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] xen: make multicall debug boot time selectable



On 7/3/24 7:56 AM, Juergen Gross wrote:

>   
>   #define MC_BATCH	32
>   
> -#define MC_DEBUG	0
> -
>   #define MC_ARGS		(MC_BATCH * 16)
>   
>   
>   struct mc_buffer {
>   	unsigned mcidx, argidx, cbidx;
>   	struct multicall_entry entries[MC_BATCH];
> -#if MC_DEBUG
> -	struct multicall_entry debug[MC_BATCH];
> -	void *caller[MC_BATCH];
> -#endif
>   	unsigned char args[MC_ARGS];
>   	struct callback {
>   		void (*fn)(void *);
> @@ -50,13 +46,84 @@ struct mc_buffer {
>   	} callbacks[MC_BATCH];
>   };
>   
> +struct mc_debug_data {
> +	struct multicall_entry debug[MC_BATCH];

'entries'? It's a mc_debug_data's copy of mc_buffer's entries.

Also, would it be better to keep these fields as a struct of scalars and 
instead have the percpu array of this struct? Otherwise there is a whole 
bunch of [MC_BATCH] arrays, all of them really indexed by the same 
value. (And while at it, there is no reason to have callbacks[MC_BATCH] 
sized like that -- it has nothing to do with batch size and can probably 
be made smaller)


> +	void *caller[MC_BATCH];
> +	size_t argsz[MC_BATCH];
> +};
> +
>   static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
> +static struct mc_debug_data __percpu *mc_debug_data;
> +static struct mc_debug_data mc_debug_data_early __initdata;

How about (I think this should work):

static struct mc_debug_data __percpu *mc_debug_data __refdata = 
&mc_debug_data_early;

Then you won't need get_mc_debug_ptr().


-boris