linux-kernel - Re: [PATCH 5/7 v6] trace, RAS: Add eMCA trace event interface

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Message-ID: <20140530092232.GA13495@gchen.bj.intel.com>
Date:	Fri, 30 May 2014 05:22:32 -0400
From:	"Chen, Gong" <gong.chen@...ux.intel.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Borislav Petkov <bp@...en8.de>, tony.luck@...el.com,
	m.chehab@...sung.com, linux-acpi@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/7 v6] trace, RAS: Add eMCA trace event interface

On Wed, May 28, 2014 at 12:56:25PM -0400, Steven Rostedt wrote:
> Instead of making that a huge string, what about a dynamic array of
> special structures?
> 
> 
> struct __attribute__((__packed__)) cper_sec_mem_rec {
> 	short type;
> 	int data;
> };
> 
> 
HI, Steven & Boris

We have two big chunk string. One for memory error location, the other
for DIMM error location. Since DIMM error location depends on some
other conditions, how about just converting memory error location
to a compact mode but leaving DIMM error location alone? 

For memory error location, I will utilize type offset to save one
more byte, furthermore, I want to drop requestor_id, responder_id
and target_id. 1) They are very rare (I've never seen them by now)
2) They are u64 but not u16. So to keep whole struct clean I want
to use following struct. We can extend it later when necessary.

struct __attribute__((__packed__)) cper_sec_mem_rec {
	u8 type;
	u16 data;
};

So whole struct is just 3 bytes. Even if all fields are valid, we
have 3 * 9 = 27 bytes in total for a record in the ring buffer.

Make sense?

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