linux-kernel - Re: [RFC PATCH v4 0/9] printk: new ringbuffer implementation

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Date:   Fri, 6 Sep 2019 19:09:43 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        John Ogness <john.ogness@...utronix.de>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v4 0/9] printk: new ringbuffer implementation

On (09/06/19 11:06), Peter Zijlstra wrote:
> Another approach is something like:
> 
> DEFINE_PER_CPU(int, printk_nest);
> DEFINE_PER_CPU(char, printk_line[4][256]);
>
> int vprintk(const char *fmt, va_list args)
> {
> 	int c, n, i;
> 	char *buf;
> 
> 	preempt_disable();
> 	i = min(3, this_cpu_inc_return(printk_nest) - 1);
> 	buf = this_cpu_ptr(printk_line[i]);
> 	n = vscnprintf(buf, 256, fmt, args);
> 
> 	c = cpu_lock();
> 	printk_buffer_store(buf, n);
> 	if (early_console)
> 		early_console->write(early_console, buf, n);
> 	cpu_unlock(c);
>
> 	this_cpu_dec(printk_nest);
> 	preempt_enable();
> 
> 	return n;
> }
> 
> Again, simple and straight forward (and I'm sure it's been mentioned
> before too).

 :)

---
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index 139c310049b1..9c73eb6259ce 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -103,7 +103,10 @@ static __printf(2, 0) int printk_safe_log_store(struct printk_safe_seq_buf *s,
        if (atomic_cmpxchg(&s->len, len, len + add) != len)
                goto again;
 
-       queue_flush_work(s);
+       if (early_console)
+               early_console->write(early_console, s->buffer + len, add);
+       else
+               queue_flush_work(s);
        return add;
 }
---

	-ss