linux-kernel - RE: [PATCH v2] printk: add option to print cpu id

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Message-ID: <D958900912E20642BCBC71664EFECE3E6DDCAC49AB@BGMAIL02.nvidia.com>
Date:	Fri, 3 Aug 2012 14:57:42 +0530
From:	Venu Byravarasu <vbyravarasu@...dia.com>
To:	Vikram Pandita <vikram.pandita@...com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"kay@...y.org" <kay@...y.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>,
	Vimarsh Zutshi <vimarsh.zutshi@...il.com>
Subject: RE: [PATCH v2] printk: add option to print cpu id

> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
> owner@...r.kernel.org] On Behalf Of Vikram Pandita
> Sent: Friday, August 03, 2012 2:46 PM
> To: gregkh@...uxfoundation.org; kay@...y.org
> Cc: linux-kernel@...r.kernel.org; Vikram Pandita; Mike Turquette; Vimarsh
> Zutshi
> Subject: [PATCH v2] printk: add option to print cpu id
> 
> From: Vikram Pandita <vikram.pandita@...com>
> 
> Introduce config option to enable CPU id reporting for printk() calls.
> 
> Example logs with this option enabled look like:
>  [1] [    2.328613] usbcore: registered new interface driver libusual
>  [1] [    2.335418] usbcore: registered new interface driver usbtest
>  [1] [    2.342803] mousedev: PS/2 mouse device common for all mice
>  [0] [    2.352600] twl_rtc twl_rtc: Power up reset detected.
>  [0] [    2.359191] twl_rtc twl_rtc: Enabling TWL-RTC
>  [1] [    2.367797] twl_rtc twl_rtc: rtc core: registered twl_rtc as rtc0
>  [1] [    2.375274] i2c /dev entries driver
>  [1] [    2.382324] Driver for 1-wire Dallas network protocol.
> 
> Its sometimes very useful to have printk also print the CPU Identifier
> that executed the call. This has helped to debug various SMP issues on
> shipping
> products.

Is it not better to have macros which will have wrapper to printk with required
debug info added? E.g. cpu# in your case.
If by default we add cupid, is it not over head in each message getting
printed with printk?

> 
> Known limitation is if the system gets preempted between function call and
> actual printk, the reported cpu-id might not be accurate. But most of the
> times its seen to give a good feel of how the N cpu's in the system are
> getting loaded.
> 
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