linux-kernel - Re: [PATCH printk v8 30/35] printk: Add helper for flush type logic

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Message-ID: <ZsWvRETyuh1Yq80j@pathway.suse.cz>
Date: Wed, 21 Aug 2024 11:11:32 +0200
From: Petr Mladek <pmladek@...e.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk v8 30/35] printk: Add helper for flush type logic

On Tue 2024-08-20 08:35:56, John Ogness wrote:
> There are many call sites where console flushing occur.
> Depending on the system state and types of consoles, the flush
> methods to use are different. A flush call site generally must
> consider:
> 
> 	@have_boot_console
> 	@have_nbcon_console
> 	@have_legacy_console
> 	@legacy_allow_panic_sync
> 	is_printk_preferred()
> 
> and take into account the current CPU state:
> 
> 	NBCON_PRIO_NORMAL
> 	NBCON_PRIO_EMERGENCY
> 	NBCON_PRIO_PANIC
> 
> in order to decide if it should:
> 
> 	flush nbcon directly via atomic_write() callback
> 	flush legacy directly via console_unlock
> 	flush legacy via offload to irq_work
> 
> All of these call sites use their own logic to make this
> decision, which is complicated and error prone. Especially
> later when two more flush methods will be introduced:
> 
> 	flush nbcon via offload to kthread
> 	flush legacy via offload to kthread
> 
> Introduce a new internal struct console_flush_type that
> specifies the flush method(s) that are available for a
> particular call site to use.

The function behaves a bit different in this version of the patch.
The paragraph should be updated according the current description
of the function:

<proposal>
Introduce a new internal struct console_flush_type that specifies which
which console flushing methods should be used in the context of
the caller.
</proposal>

> Introduce a helper function to fill out console_flush_type to
> be used for flushing call sites.
> 
> Replace the logic of all flushing call sites to use the new
> helper. 

I would add:

<proposal>
This change standardizes behavior, leading to both fixes and optimizations
across various call sites. For instance, in console_cpu_notify(), the new
logic ensures that nbcon consoles are flushed when they aren’t managed
by the legacy loop. Similarly, in console_flush_on_panic(), the system
no longer needs to flush nbcon consoles if none are present.
</proposal>

> Signed-off-by: John Ogness <john.ogness@...utronix.de>

With the above changes:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr