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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAFm5wm2Z+FyVqG5oMWiEmZ8Je88hJ-cyDXmJw0wp4mqA-X9eYg@mail.gmail.com>
Date:	Fri, 3 Aug 2012 02:36:30 -0700
From:	"Pandita, Vikram" <vikram.pandita@...com>
To:	Venu Byravarasu <vbyravarasu@...dia.com>
Cc:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"kay@...y.org" <kay@...y.org>,
	"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

Venu

On Fri, Aug 3, 2012 at 2:32 AM, Venu Byravarasu <vbyravarasu@...dia.com> wrote:
>
>> -----Original Message-----
>> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
>> owner@...r.kernel.org] On Behalf Of Venu Byravarasu
>> Sent: Friday, August 03, 2012 2:58 PM
>> To: Vikram Pandita; gregkh@...uxfoundation.org; kay@...y.org
>> Cc: linux-kernel@...r.kernel.org; Mike Turquette; Vimarsh Zutshi
>> 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.
>>
>
> As having Macro locally in the file of interest would serve the purpose,
> Why to change the printk code?

As stated, the logic followed is exactly similar to well proven and
approved way to handle printk time stamp: CONFIG_PRINTK_TIME
Its an overhead on the system that enables the config option:
CONFIG_PRINTK_CPUID
Otherwise the system remains as is.

To gain insight on SMP system logging behavior, the price to pay is
the extra 4 chars per printk line,
just like printk-time adds 15 chars to each line. Both options can be
disabled as desired.

So i am not sure what kind of option you are proposing?
Do u imply PRINTK_TIME is not right then?


>
>> 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@...r.kernel.org
>> 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@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/