From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Daniel Wang <wonderfly@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
Jiri Slaby <jslaby@suse.com>, Peter Feiner <pfeiner@google.com>,
linux-serial@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [RFC PATCH v1 00/25] printk: new implementation
Date: Wed, 13 Feb 2019 10:31:01 +0900 [thread overview]
Message-ID: <20190213013101.GA8097@jagdpanzerIV> (raw)
In-Reply-To: <20190212143003.48446-1-john.ogness@linutronix.de>
On (02/12/19 15:29), John Ogness wrote:
>
> 1. The printk buffer is protected by a global raw spinlock for readers
> and writers. This restricts the contexts that are allowed to
> access the buffer.
[..]
> 2. Because of #1, NMI and recursive contexts are handled by deferring
> logging/printing to a spinlock-safe context. This means that
> messages will not be visible if (for example) the kernel dies in
> NMI context and the irq_work mechanism does not survive.
panic() calls printk_safe_flush_on_panic(), which iterates all per-CPU
buffers and moves data to the main logbuf; so then we can flush pending
logbuf message
panic()
printk_safe_flush_on_panic();
console_flush_on_panic();
We don't really use irq_work mechanism for that.
> 3. Because of #1, when *not* using features such as PREEMPT_RT, large
> latencies exist when printing to slow consoles.
Because of #1? I'm not familiar with PREEMPT_RT; but logbuf spinlock
should be unlocked while we print messages to slow consoles
(call_consoles_drivers() is protected by console_sem, not logbuf
lock).
So it's
spin_lock_irqsave(logbuf);
vsprintf();
memcpy();
spin_unlock_irqrestore(logbuf);
console_trylock();
for (;;)
call_console_drivers();
// console_owner handover
console_unlock();
Do you see large latencies because of logbuf spinlock?
> 5. Printing to consoles is the responsibility of the printk caller
> and that caller may be required to print many messages that other
> printk callers inserted. Because of this there can be enormous
> variance in the runtime of a printk call.
That's complicated. Steven's console_owner handover patch makes
printk() more fair. We can have "winner takes it all" scenarios,
but significantly less often, IMO. Do you have any data that
suggest otherwise?
> 7. Loglevel INFO is handled the same as ERR. There seems to be an
> endless effort to get printk to show _all_ messages as quickly as
> possible in case of a panic (i.e. printing from any context), but
> at the same time try not to have printk be too intrusive for the
> callers. These are conflicting requirements that lead to a printk
> implementation that does a sub-optimal job of satisfying both
> sides.
Per my experience, fully preemptible "print it sometime maybe"
printk() does not work equally well for everyone.
-ss
next prev parent reply other threads:[~2019-02-13 1:31 UTC|newest]
Thread overview: 147+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-12 14:29 [RFC PATCH v1 00/25] printk: new implementation John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 01/25] printk-rb: add printk ring buffer documentation John Ogness
2019-02-12 14:45 ` Greg Kroah-Hartman
2019-02-12 14:29 ` [RFC PATCH v1 02/25] printk-rb: add prb locking functions John Ogness
2019-02-13 15:45 ` Petr Mladek
2019-02-13 21:39 ` John Ogness
2019-02-14 10:33 ` Petr Mladek
2019-02-14 12:10 ` John Ogness
2019-02-15 10:26 ` Petr Mladek
2019-02-15 10:56 ` John Ogness
2019-03-07 2:12 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 03/25] printk-rb: define ring buffer struct and initializer John Ogness
2019-02-12 14:46 ` Greg Kroah-Hartman
2019-02-14 12:46 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 04/25] printk-rb: add writer interface John Ogness
2019-02-14 15:16 ` Petr Mladek
2019-02-14 23:36 ` John Ogness
2019-02-15 1:19 ` John Ogness
2019-02-15 13:47 ` Petr Mladek
2019-02-17 1:32 ` John Ogness
2019-02-21 13:51 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 05/25] printk-rb: add basic non-blocking reading interface John Ogness
2019-02-18 12:54 ` Petr Mladek
2019-02-19 21:44 ` John Ogness
2019-02-21 16:22 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 06/25] printk-rb: add blocking reader support John Ogness
2019-02-18 14:05 ` Petr Mladek
2019-02-19 21:47 ` John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 07/25] printk-rb: add functionality required by printk John Ogness
2019-02-12 17:15 ` Linus Torvalds
2019-02-13 9:20 ` John Ogness
2019-02-18 15:59 ` Petr Mladek
2019-02-19 22:08 ` John Ogness
2019-02-22 9:58 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 08/25] printk: add ring buffer and kthread John Ogness
2019-02-12 15:47 ` Sergey Senozhatsky
2019-02-19 13:54 ` Petr Mladek
2019-03-04 7:38 ` Sergey Senozhatsky
2019-03-04 10:00 ` Sergey Senozhatsky
2019-03-04 11:07 ` Sergey Senozhatsky
2019-03-05 21:00 ` John Ogness
2019-03-06 15:57 ` Petr Mladek
2019-03-06 21:17 ` John Ogness
2019-03-06 22:22 ` John Ogness
2019-03-07 6:41 ` Sergey Senozhatsky
2019-03-07 6:51 ` Sergey Senozhatsky
2019-03-07 12:50 ` Petr Mladek
2019-03-07 5:15 ` Sergey Senozhatsky
2019-03-11 10:51 ` John Ogness
2019-03-12 9:58 ` Sergey Senozhatsky
2019-03-12 10:30 ` Petr Mladek
2019-03-07 12:06 ` John Ogness
2019-03-08 1:31 ` Sergey Senozhatsky
2019-03-08 10:04 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 09/25] printk: remove exclusive console hack John Ogness
2019-02-19 14:03 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 10/25] printk: redirect emit/store to new ringbuffer John Ogness
2019-02-20 9:01 ` Petr Mladek
2019-02-20 21:25 ` John Ogness
2019-02-22 14:43 ` Petr Mladek
2019-02-22 15:06 ` John Ogness
2019-02-22 15:25 ` Petr Mladek
2019-02-25 12:11 ` Petr Mladek
2019-02-25 16:41 ` John Ogness
2019-02-26 9:45 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 11/25] printk_safe: remove printk safe code John Ogness
2019-02-22 10:37 ` Petr Mladek
2019-02-22 13:38 ` John Ogness
2019-02-22 15:15 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 12/25] printk: minimize console locking implementation John Ogness
2019-02-25 13:44 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 13/25] printk: track seq per console John Ogness
2019-02-25 14:59 ` Petr Mladek
2019-02-26 8:45 ` John Ogness
2019-02-26 13:11 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 14/25] printk: do boot_delay_msec inside printk_delay John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 15/25] printk: print history for new consoles John Ogness
2019-02-26 14:58 ` Petr Mladek
2019-02-26 15:22 ` John Ogness
2019-02-27 9:02 ` Petr Mladek
2019-02-27 10:02 ` John Ogness
2019-02-27 13:12 ` Petr Mladek
2019-03-04 9:24 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 16/25] printk: implement CON_PRINTBUFFER John Ogness
2019-02-26 15:38 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 17/25] printk: add processor number to output John Ogness
2019-02-13 22:29 ` John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 18/25] console: add write_atomic interface John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 19/25] printk: introduce emergency messages John Ogness
2019-03-07 7:30 ` Sergey Senozhatsky
2019-03-08 10:31 ` Petr Mladek
2019-03-11 12:04 ` John Ogness
2019-03-12 2:51 ` Sergey Senozhatsky
2019-03-12 2:58 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 20/25] serial: 8250: implement write_atomic John Ogness
2019-02-27 9:46 ` Petr Mladek
2019-02-27 10:32 ` John Ogness
2019-02-27 13:55 ` Petr Mladek
2019-03-08 4:05 ` John Ogness
2019-03-08 4:17 ` John Ogness
2019-03-08 10:28 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 21/25] printk: implement KERN_CONT John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 22/25] printk: implement /dev/kmsg John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 23/25] printk: implement syslog John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 24/25] printk: implement kmsg_dump John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 25/25] printk: remove unused code John Ogness
2019-03-08 14:02 ` Sebastian Andrzej Siewior
2019-03-11 2:46 ` Sergey Senozhatsky
2019-03-11 8:18 ` Sebastian Andrzej Siewior
2019-03-12 9:38 ` Petr Mladek
2019-02-13 1:31 ` Sergey Senozhatsky [this message]
2019-02-13 13:43 ` [RFC PATCH v1 00/25] printk: new implementation John Ogness
2019-03-04 6:39 ` Sergey Senozhatsky
2019-02-13 1:41 ` Sergey Senozhatsky
2019-02-13 14:15 ` John Ogness
2019-03-04 5:31 ` Sergey Senozhatsky
2019-02-13 2:55 ` Sergey Senozhatsky
2019-02-13 14:43 ` John Ogness
2019-03-04 5:23 ` Sergey Senozhatsky
2019-03-07 9:53 ` John Ogness
2019-03-08 10:00 ` Petr Mladek
2019-03-11 10:54 ` Sergey Senozhatsky
2019-03-12 12:38 ` Petr Mladek
2019-03-12 15:15 ` John Ogness
2019-03-13 2:15 ` Sergey Senozhatsky
2019-03-13 8:19 ` John Ogness
2019-03-13 8:40 ` Sebastian Siewior
2019-03-13 9:27 ` Sergey Senozhatsky
2019-03-13 10:06 ` Sergey Senozhatsky
2019-03-14 9:27 ` Petr Mladek
2019-03-13 8:46 ` Sergey Senozhatsky
2019-03-14 9:14 ` Petr Mladek
2019-03-14 9:35 ` John Ogness
2019-03-13 2:00 ` Sergey Senozhatsky
2019-02-13 16:54 ` David Laight
2019-02-13 22:20 ` John Ogness
2020-01-20 23:05 ` Eugeniu Rosca
2020-01-21 23:56 ` John Ogness
2020-01-22 2:34 ` Eugeniu Rosca
2020-01-22 7:31 ` Geert Uytterhoeven
2020-01-22 16:58 ` Eugeniu Rosca
2020-01-22 19:48 ` Geert Uytterhoeven
2020-01-24 16:09 ` Eugeniu Rosca
2020-01-27 12:32 ` Petr Mladek
2020-01-27 13:45 ` Eugeniu Rosca
2020-01-22 10:33 ` John Ogness
2020-01-24 12:13 ` Eugeniu Rosca
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