linux-kernel - Re: [PATCH -v4] x86: MCE: Re-implement MCE log ring buffer as per-CPU ring buffer

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Date:	Fri, 05 Jun 2009 16:39:34 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <ak@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -v4] x86: MCE: Re-implement MCE log ring buffer as
 per-CPU ring buffer

On Fri, 2009-06-05 at 16:28 +0800, Hidetoshi Seto wrote:
> Huang Ying wrote:
> > On Fri, 2009-06-05 at 15:01 +0800, Hidetoshi Seto wrote:
> >> Huang Ying wrote:
> >>>  struct mce_log {
> >>> -	char signature[12]; /* "MACHINECHECK" */
> >>> +	char signature[12]; /* "MACHINECHEC2" */
> >>>  	unsigned len;	    /* = MCE_LOG_LEN */
> >>> -	unsigned next;
> >>>  	unsigned flags;
> >>>  	unsigned pad0;
> >>> -	struct mce entry[MCE_LOG_LEN];
> >>> +	struct mce_log_cpu *mcelog_cpus;
> >>>  };
> >> What is this *mcelog_cpus to be used for?
> >> It seems it will point one of per-CPU buffers (maybe cpu#0's buffer)
> >> if I have read the following mce_log_init() correctly.
> > 
> > It is mainly used by something like kdump, which can search
> > "MACHINECHEC2", and analyze mce_log. mcelog_cpus can help kdump find the
> > real mcelog storage.
> 
> Hum, but it help tools only to find one of buffers, not to find all.
> 
> I think it would be better help for tools if we have another signature
> on struct mce_log_cpu, e.g.: 
> 
>  +struct mce_log_cpu {
> + 	char signature[**];	/* "MCE_LOG_CPU_VER_1" or so */
> +	__u32 cpuid;		/* cpuid or extcpu, same as struct mce */
>  +	int head;
>  +	int tail;
>  +	unsigned long flags;
>  +	struct mce entry[MCE_LOG_LEN];
>  +};
> 
> How about this?

+	mcelog.mcelog_cpus = &per_cpu_var(mce_log_cpus);

So mcelog.mcelog_cpus are pointed to the buffers of all CPUs, not just
that of one CPU. You can find them by analyzing PER cpu data structure.

Best Regards,
Huang Ying


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