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

From: Venu Byravarasu
Date: Fri Aug 03 2012 - 05:32:24 EST



> -----Original Message-----
> From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Venu Byravarasu
> Sent: Friday, August 03, 2012 2:58 PM
> To: Vikram Pandita; gregkh@xxxxxxxxxxxxxxxxxxx; kay@xxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; Mike Turquette; Vimarsh Zutshi
> Subject: RE: [PATCH v2] printk: add option to print cpu id
>
> > -----Original Message-----
> > From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel-
> > owner@xxxxxxxxxxxxxxx] On Behalf Of Vikram Pandita
> > Sent: Friday, August 03, 2012 2:46 PM
> > To: gregkh@xxxxxxxxxxxxxxxxxxx; kay@xxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx; Vikram Pandita; Mike Turquette; Vimarsh
> > Zutshi
> > Subject: [PATCH v2] printk: add option to print cpu id
> >
> > From: Vikram Pandita <vikram.pandita@xxxxxx>
> >
> > 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.
>

As having Macro locally in the file of interest would serve the purpose,
Why to change the printk code?

> 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.
> >
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/