From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: linux.git: printk() problem
Date: Tue, 25 Oct 2016 10:42:56 -0400 [thread overview]
Message-ID: <20161025144256.ngfxchitby4xpxno@home.goodmis.org> (raw)
In-Reply-To: <CA+55aFw1Z95Lfefr1PfZW17qj9zjv+-bZ-oPESTNk+tbAEVrhQ@mail.gmail.com>
On Sun, Oct 23, 2016 at 11:11:18AM -0700, Linus Torvalds wrote:
>
> For example, one of the really historical uses for partial lines is this:
>
> pr_info("Checking 'hlt' instruction... ");
>
> if (!boot_cpu_data.hlt_works_ok) {
> pr_cont("disabled\n");
> return;
> }
> halt();
> halt();
> halt();
> halt();
> pr_cont("OK\n");
>
> and the point was that there used to be some really old i386 machines
> that hung on the "hlt" instruction (probably not because of a CPU bug,
> but because of either power supply issues or some DMA issues).
>
> To support that, we really *had* to print out the continuation lines
> even when they were partial. And that complicates the printk logic a
> lot.
Note, my ftrace start up tests still does exactly this (e.g.):
pr_info("Testing dynamic ftrace ops: #%d: ", cnt);
[ do lots of testing ]
printk(KERN_CONT "PASSED\n");
Previously a change was made to buffer lines without \n, and I wasted an
entire day debugging why a crash happened because I was looking at the wrong
test.
-- Steve
>
> Now, that "hlt" case is long long gone, and maybe we should just say
> "screw that". It would be really quite easy to say "we don't print out
> continuation lines immediately, we just buffer them for 0.1s instead,
> and KERN_CONT only works for things that really happen more or less
> immediately".
>
> Maybe that really is the right answer. Because the original cause of
> us having to bend over backwards in this case is really no longer
> there. And it would simplify printk a *lot*.
>
> Let me whip up a minimal patch for you to try.
prev parent reply other threads:[~2016-10-25 14:43 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-12 13:30 linux.git: printk() problem Tetsuo Handa
2016-10-12 14:35 ` Michal Hocko
2016-10-12 16:08 ` Joe Perches
2016-10-13 6:26 ` Michal Hocko
2016-10-13 9:29 ` Joe Perches
2016-10-13 10:04 ` Michal Hocko
2016-10-13 10:20 ` Joe Perches
2016-10-13 11:06 ` Michal Hocko
2016-10-12 15:47 ` Linus Torvalds
2016-10-12 16:16 ` Joe Perches
2016-10-12 16:54 ` Linus Torvalds
2016-10-12 18:50 ` [PATCH] acpi_os_vprintf: Use printk_get_level() to avoid unnecessary KERN_CONT Joe Perches
2016-10-13 21:59 ` Rafael J. Wysocki
2016-10-23 9:22 ` linux.git: printk() problem Geert Uytterhoeven
2016-10-23 18:11 ` Linus Torvalds
2016-10-23 19:06 ` Joe Perches
2016-10-23 19:32 ` Linus Torvalds
2016-10-23 19:46 ` Linus Torvalds
2016-10-24 11:15 ` Geert Uytterhoeven
2016-10-24 14:08 ` Sergey Senozhatsky
2016-10-24 14:23 ` Sergey Senozhatsky
2016-10-24 17:54 ` Linus Torvalds
2016-10-24 17:55 ` Linus Torvalds
2016-10-25 1:55 ` Sergey Senozhatsky
2016-10-25 2:06 ` Linus Torvalds
2016-10-25 2:22 ` Linus Torvalds
2016-10-25 4:06 ` Sergey Senozhatsky
2016-10-25 4:13 ` Joe Perches
2016-10-25 4:15 ` Linus Torvalds
2016-10-25 4:44 ` Sergey Senozhatsky
2016-10-25 14:44 ` Petr Mladek
2016-11-09 15:47 ` Petr Mladek
2016-10-25 2:24 ` Sergey Senozhatsky
2016-10-23 20:33 ` Joe Perches
2016-10-23 21:13 ` Linus Torvalds
2016-10-25 14:42 ` Steven Rostedt [this message]
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