linux-kernel - Re: [RFC PATCH] printk: Change timestamp to triplet as mono, boot and real

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Date:   Thu, 13 Aug 2020 20:31:55 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Orson Zhai <orsonzhai@...il.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, zhang.lyra@...il.com,
        ruifeng.zhang1@...soc.com, cixi.geng1@...soc.com,
        Orson Zhai <orson.zhai@...soc.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Steven Sistare <steven.sistare@...cle.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jon DeVree <nuxi@...lt24.org>,
        Salvatore Bonaccorso <carnil@...ian.org>,
        John Ogness <john.ogness@...utronix.de>
Subject: Re: [RFC PATCH] printk: Change timestamp to triplet as mono, boot
 and real

On (20/08/13 12:22), Petr Mladek wrote:
>
>   + would take more space (prefix + text vs. binary representation)

Dict buffer is allocated regardless of how we use it, and only printks
from drivers/* (dev_printk*) add dict payload. It might be the case
that on some (if not most) systems dict pages are not used 90% of times
(if not 99%).

>   + not reliable because dict is currently dropped when no space

Well, in the perfect world this is a problem, but "maybe not having
alternative timestamps sometimes" can be OK approach for people who
wants to use those triplet timestamps.

But, in general, how real this problem is? What I sae so far (on my boxes)
was that printk messages are longer than dict payload.

Example:

6,223,93298,-,caller=T1;acpi PNP0A08:00: _OSC: OS supports [Segments MSI HPX-Type3]
 SUBSYSTEM=acpi
 DEVICE=+acpi:PNP0A08:00
6,224,93413,-,caller=T1;acpi PNP0A08:00: _OSC: not requesting OS control; OS requires [ExtendedConfig ASPM ClockPM MSI]
 SUBSYSTEM=acpi
 DEVICE=+acpi:PNP0A08:00
6,225,93540,-,caller=T1;PCI host bridge to bus 0000:00
6,226,93541,-,caller=T1;pci_bus 0000:00: root bus resource [io  0x0000-0x0cf7 window]
 SUBSYSTEM=pci_bus
 DEVICE=+pci_bus:0000:00

It might be the case, that overflowing dict buffer, without first overflowing
printk buffer, can be rather challenging.

>   + it would make the controversial dictionary feature more important

Yes. But, for the time being, this controversial dict feature allocates
pages for dict buffer anyway.

	-ss