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From: Petr Mladek <pmladek@suse.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Dmitriy Vyukov <dvyukov@google.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Alexander Potapenko <glider@google.com>,
	Fengguang Wu <fengguang.wu@intel.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH 3/3] lockdep: Use line-buffered printk() for lockdep messages.
Date: Fri, 23 Nov 2018 13:52:19 +0100	[thread overview]
Message-ID: <20181123125219.k5flkypofll7jwtr@pathway.suse.cz> (raw)
In-Reply-To: <2d0d1f60-d8b6-41e0-6845-0eb62f211e40@i-love.sakura.ne.jp>

On Sat 2018-11-10 17:52:17, Tetsuo Handa wrote:
> On 2018/11/10 0:43, Petr Mladek wrote:
> > On Fri 2018-11-09 18:55:26, Tetsuo Handa wrote:
> >> How early_printk requirement affects line buffered printk() API?
> >>
> >> I don't think it is impossible to convert from
> >>
> >>      printk("Testing feature XYZ..");
> >>      this_may_blow_up_because_of_hw_bugs();
> >>      printk(KERN_CONT " ... ok\n");
> >>
> >> to
> >>
> >>      printk("Testing feature XYZ:\n");
> >>      this_may_blow_up_because_of_hw_bugs();
> >>      printk("Testing feature XYZ.. ... ok\n");
> >>
> >> in https://lore.kernel.org/lkml/CA+55aFwmwdY_mMqdEyFPpRhCKRyeqj=+aCqe5nN108v8ELFvPw@mail.gmail.com/ .
> > 
> > I just wonder how this pattern is common. I have tried but I failed
> > to find any instance.
> > 
> > This problem looks like a big argument against explicit buffers.
> > But I wonder if it is real.
> 
> An example of boot up messages where buffering makes difference.
> 
> Vanilla:
> 
> [    0.260459] smp: Bringing up secondary CPUs ...
> [    0.269595] x86: Booting SMP configuration:
> [    0.270461] .... node  #0, CPUs:      #1
> [    0.066578] Disabled fast string operations
> [    0.066578] mce: CPU supports 0 MCE banks
> [    0.066578] smpboot: CPU 1 Converting physical 2 to logical package 1
> [    0.342569]  #2
> [    0.066578] Disabled fast string operations
> [    0.066578] mce: CPU supports 0 MCE banks
> [    0.066578] smpboot: CPU 2 Converting physical 4 to logical package 2
> [    0.413442]  #3
> [    0.066578] Disabled fast string operations
> [    0.066578] mce: CPU supports 0 MCE banks
> [    0.066578] smpboot: CPU 3 Converting physical 6 to logical package 3
> [    0.476562] smp: Brought up 1 node, 4 CPUs
> [    0.477477] smpboot: Max logical packages: 8
> [    0.477514] smpboot: Total of 4 processors activated (22691.70 BogoMIPS)
> 
> With try_buffered_printk() patch:
> 
> [    0.279768] smp: Bringing up secondary CPUs ...
> [    0.288825] x86: Booting SMP configuration:
> [    0.066748] Disabled fast string operations
> [    0.066748] mce: CPU supports 0 MCE banks
> [    0.066748] smpboot: CPU 1 Converting physical 2 to logical package 1
> [    0.066748] Disabled fast string operations
> [    0.066748] mce: CPU supports 0 MCE banks
> [    0.066748] smpboot: CPU 2 Converting physical 4 to logical package 2
> [    0.066748] Disabled fast string operations
> [    0.066748] mce: CPU supports 0 MCE banks
> [    0.066748] smpboot: CPU 3 Converting physical 6 to logical package 3
> [    0.495862] .... node  #0, CPUs:      #1 #2 #3\x016smp: Brought up 1 node, 4 CPUs
> [    0.496833] smpboot: Max logical packages: 8
> [    0.497609] smpboot: Total of 4 processors activated (22665.22 BogoMIPS)
> 
> 
> 
> Hmm, arch/x86/kernel/smpboot.c is not emitting '\n' after #num
> 
>         if (system_state < SYSTEM_RUNNING) {
>                 if (node != current_node) {
>                         if (current_node > (-1))
>                                 pr_cont("\n");
>                         current_node = node;
> 
>                         printk(KERN_INFO ".... node %*s#%d, CPUs:  ",
>                                node_width - num_digits(node), " ", node);
>                 }
> 
>                 /* Add padding for the BSP */
>                 if (cpu == 1)
>                         pr_cont("%*s", width + 1, " ");
> 
>                 pr_cont("%*s#%d", width - num_digits(cpu), " ", cpu);
> 
>         } else
>                 pr_info("Booting Node %d Processor %d APIC 0x%x\n",
>                         node, cpu, apicid);
> 
> and causing
> 
>         pr_info("Brought up %d node%s, %d CPU%s\n",
>                 num_nodes, (num_nodes > 1 ? "s" : ""),
>                 num_cpus,  (num_cpus  > 1 ? "s" : ""));
> 
> line to be concatenated to previous line.
> Maybe disable try_buffered_printk() if system_state !=
> SYSTEM_RUNNING ?

We need to solve continuous lines also during boot. Also similar
problems might be in the code that is called in SYSTEM_RUNNING state.

This is yet another clue that try_buffered_printk() approach is not
that good idea.

Best Regards,
Petr

  reply	other threads:[~2018-11-23 12:52 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-02 13:31 [PATCH v6 1/3] printk: Add line-buffered printk() API Tetsuo Handa
2018-11-02 13:31 ` [PATCH 2/3] mm: Use line-buffered printk() for show_free_areas() Tetsuo Handa
2018-11-07 14:07   ` Petr Mladek
2018-11-02 13:31 ` [PATCH 3/3] lockdep: Use line-buffered printk() for lockdep messages Tetsuo Handa
2018-11-02 13:36   ` Peter Zijlstra
2018-11-03  2:00     ` Tetsuo Handa
2018-11-06  8:38     ` Petr Mladek
2018-11-06  9:05       ` Sergey Senozhatsky
2018-11-06 12:57         ` Petr Mladek
2018-11-06  9:56       ` Tetsuo Handa
2018-11-07 15:19   ` Petr Mladek
2018-11-08  4:45     ` Sergey Senozhatsky
2018-11-08 11:37       ` Tetsuo Handa
2018-11-09  6:12         ` Sergey Senozhatsky
2018-11-09  9:55           ` Tetsuo Handa
2018-11-09 15:43             ` Petr Mladek
2018-11-10  2:42               ` Tetsuo Handa
2018-11-23 12:46                 ` Petr Mladek
2018-11-23 13:12                   ` Tetsuo Handa
2018-11-23 15:56                   ` Steven Rostedt
2018-11-24  0:24                     ` Tetsuo Handa
2018-11-26  4:34                       ` Sergey Senozhatsky
2018-11-28 13:29                     ` David Laight
2018-11-29 10:09                       ` Tetsuo Handa
2018-11-30 16:01                         ` Petr Mladek
2018-11-10  8:52               ` Tetsuo Handa
2018-11-23 12:52                 ` Petr Mladek [this message]
2018-11-09 14:08           ` Linus Torvalds
2018-11-09 14:42             ` Steven Rostedt
2018-11-08 11:53       ` Petr Mladek
2018-11-08 12:44         ` Sergey Senozhatsky
2018-11-08 14:21           ` Sergey Senozhatsky
2018-11-09  9:54     ` Tetsuo Handa
2018-11-02 14:40 ` [PATCH v6 1/3] printk: Add line-buffered printk() API Matthew Wilcox
2018-11-03  1:55   ` Tetsuo Handa
2018-11-02 18:12 ` kbuild test robot
2018-11-02 18:12   ` kbuild test robot
2018-11-06 14:35 ` Sergey Senozhatsky
2018-11-07 10:21   ` Petr Mladek
2018-11-07 12:54     ` Tetsuo Handa
2018-11-08  2:21     ` Sergey Senozhatsky
2018-11-08 11:24       ` Petr Mladek
2018-11-08 11:46         ` Tetsuo Handa
2018-11-08 12:30         ` Sergey Senozhatsky
2018-11-09 14:10           ` Petr Mladek
2018-11-12  7:59             ` Sergey Senozhatsky
2018-11-12 10:42               ` Tetsuo Handa
2018-11-17 10:14               ` Tetsuo Handa
2018-11-07 10:52   ` Tetsuo Handa
2018-11-07 11:01     ` David Laight
2018-11-07 12:00       ` Petr Mladek
2018-11-07 11:45     ` Petr Mladek
2018-11-08  2:30     ` Sergey Senozhatsky
2018-11-07 13:41 ` Petr Mladek
2018-11-07 14:06 ` Petr Mladek

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