From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH printk v1 06/13] printk: refactor and rework printing logic
Date: Wed, 02 Mar 2022 17:16:37 +0106 [thread overview]
Message-ID: <87sfs0gwsi.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <Yg0bjsObmb9Zp1YP@alley>
On 2022-02-16, Petr Mladek <pmladek@suse.com> wrote:
>> Refactor/rework printing logic in order to prepare for moving to threaded
>> console printing.
>>
>> - Move @console_seq into struct console so that the current "position" of
>> each console can be tracked individually.
>>
>> - Move @console_dropped into struct console so that the current drop count
>> of each console can be tracked individually.
>>
>> - Modify printing logic so that each console independently loads, prepares,
>> prints, and delays its next record.
>>
>> - Remove exclusive_console logic. Since console positions are handled
>> independently, replaying past records occurs naturally.
>
> It would be great to say if it has any behavior change.
>
> There is one change caused by moving printk_delay(). I suggest to do
> it in a separate patch. See below for more details.
OK. I will do it in a separate patch.
> Another change is that console replaying the log (former exclusive
> console) does not longer block other consoles. New messages appear
> on other consoles while the newly added console is still replaying.
>
> Otherwise it should not change the existing behavior.
OK, I will mention behavior changes.
>> --- a/kernel/printk/printk.c
>> +++ b/kernel/printk/printk.c
>> @@ -2560,31 +2524,167 @@ int is_console_locked(void)
>> EXPORT_SYMBOL(is_console_locked);
>>
>> /*
>> - * Check if we have any console that is capable of printing while cpu is
>> - * booting or shutting down. Requires console_sem.
>> + * Check if the given console is currently capable and allowed to print
>> + * records.
>> + *
>> + * Requires the console_lock.
>> */
>> -static int have_callable_console(void)
>> +static inline bool console_is_usable(struct console *con)
>> {
>> - struct console *con;
>> + if (!(con->flags & CON_ENABLED))
>> + return false;
>>
>> - for_each_console(con)
>> - if ((con->flags & CON_ENABLED) &&
>> - (con->flags & CON_ANYTIME))
>> - return 1;
>> + if (!con->write)
>> + return false;
>>
>> - return 0;
>> + /*
>> + * Console drivers may assume that per-cpu resources have been
>> + * allocated. So unless they're explicitly marked as being able to
>> + * cope (CON_ANYTIME) don't call them until per-cpu resources have
>> + * been allocated.
>> + */
>> + if (!printk_percpu_data_ready() &&
>> + !(con->flags & CON_ANYTIME))
>> + return false;
>
> Just for record. I am not completely sure about this check. It is
> being discussed in the 3rd patch.
Yes. In that discussion I mention that I will change it for v2.
>> +
>> + return true;
>> +}
>> +
>> +static void __console_unlock(void)
>> +{
>> + console_locked = 0;
>> + up_console_sem();
>> +}
>> +
>> +/*
>> + * Print one record for the given console. The record printed is whatever
>> + * record is the next available record for the given console.
>> + *
>> + * Requires the console_lock.
>> + *
>> + * Returns false if the given console has no next record to print, otherwise
>> + * true.
>> + *
>> + * @handover will be set to true if a printk waiter has taken over the
>> + * console_lock, in which case the caller is no longer holding the
>> + * console_lock. Otherwise it is set to false.
>> + */
>> +static bool console_emit_next_record(struct console *con, bool *handover)
>> +{
>> + static char ext_text[CONSOLE_EXT_LOG_MAX];
>> + static char text[CONSOLE_LOG_MAX];
>> + struct printk_info info;
>> + struct printk_record r;
>> + unsigned long flags;
>> + char *write_text;
>> + size_t len;
>> +
>> + prb_rec_init_rd(&r, &info, text, sizeof(text));
>> +
>> + *handover = false;
>> +
>> + if (!prb_read_valid(prb, con->seq, &r))
>> + return false;
>> +
>> + if (con->seq != r.info->seq) {
>> + con->dropped += r.info->seq - con->seq;
>> + con->seq = r.info->seq;
>> + }
>> +
>> + /* Skip record that has level above the console loglevel. */
>> + if (suppress_message_printing(r.info->level)) {
>> + con->seq++;
>> + goto skip;
>> + }
>> +
>> + if (con->flags & CON_EXTENDED) {
>> + write_text = &ext_text[0];
>> + len = info_print_ext_header(ext_text, sizeof(ext_text), r.info);
>> + len += msg_print_ext_body(ext_text + len, sizeof(ext_text) - len,
>> + &r.text_buf[0], r.info->text_len, &r.info->dev_info);
>> + } else {
>> + write_text = &text[0];
>> + len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
>> + }
>> +
>> + /*
>> + * While actively printing out messages, if another printk()
>> + * were to occur on another CPU, it may wait for this one to
>> + * finish. This task can not be preempted if there is a
>> + * waiter waiting to take over.
>> + *
>> + * Interrupts are disabled because the hand over to a waiter
>> + * must not be interrupted until the hand over is completed
>> + * (@console_waiter is cleared).
>> + */
>> + printk_safe_enter_irqsave(flags);
>> + console_lock_spinning_enable();
>> +
>> + stop_critical_timings(); /* don't trace print latency */
>> + call_console_driver(con, write_text, len);
>> + start_critical_timings();
>> +
>> + con->seq++;
>> +
>> + *handover = console_lock_spinning_disable_and_check();
>> + printk_safe_exit_irqrestore(flags);
>> +
>> + printk_delay(r.info->level);
>
> This is the desired behavior when the messages are printed by
> kthreads. Though, it will delay the output more times when
> more consoles are registered and the messages are printed
> synchronously from console_unlock().
>
> It is probably not super important. The delay is used only
> for debugging and people probably adjust it by a personal
> taste.
>
> Anyway, we should not hide this behavior change in this hude patch.
> IMHO, it is perfectly fine to keep the delay in vprintk_emit() for
> now. We could move it into console_flush_all() and kthread loops
> in a separate patch later.
OK, I will move it in a separate patch. And I will move it into the
kthreads and console_flush_all() so that the delay is only once per
successful output.
John
next prev parent reply other threads:[~2022-03-02 16:10 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-07 19:43 [PATCH printk v1 00/13] implement threaded console printing John Ogness
2022-02-07 19:43 ` [PATCH printk v1 01/13] printk: rename cpulock functions John Ogness
2022-02-11 12:44 ` Petr Mladek
2022-02-11 14:42 ` John Ogness
2022-02-11 20:57 ` Steven Rostedt
2022-02-11 21:04 ` Peter Zijlstra
2022-02-15 9:32 ` Petr Mladek
2022-02-15 9:13 ` Petr Mladek
2022-02-14 6:49 ` Sergey Senozhatsky
2022-02-14 9:45 ` John Ogness
2022-02-15 9:29 ` Petr Mladek
2022-02-16 3:27 ` Sergey Senozhatsky
2022-02-17 14:34 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 02/13] printk: cpu sync always disable interrupts John Ogness
2022-02-11 12:58 ` Petr Mladek
2022-02-14 6:36 ` Sergey Senozhatsky
2022-02-07 19:43 ` [PATCH printk v1 03/13] printk: use percpu flag instead of cpu_online() John Ogness
2022-02-11 16:05 ` Petr Mladek
2022-02-14 7:08 ` Sergey Senozhatsky
2022-02-14 7:35 ` Sergey Senozhatsky
2022-02-15 10:38 ` Petr Mladek
2022-02-16 3:29 ` Sergey Senozhatsky
2022-03-02 14:21 ` John Ogness
2022-03-04 15:56 ` Petr Mladek
2022-03-05 17:05 ` Jason A. Donenfeld
2022-03-07 16:14 ` Petr Mladek
2022-02-16 13:58 ` two locations: was: " Petr Mladek
2022-03-02 14:49 ` John Ogness
2022-03-04 16:14 ` Petr Mladek
2022-03-07 10:06 ` John Ogness
2022-03-08 16:08 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 04/13] printk: get caller_id/timestamp after migration disable John Ogness
2022-02-15 5:53 ` Sergey Senozhatsky
2022-02-15 11:56 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 05/13] printk: call boot_delay_msec() in printk_delay() John Ogness
2022-02-15 5:58 ` Sergey Senozhatsky
2022-02-15 14:59 ` Petr Mladek
2022-02-16 3:21 ` Sergey Senozhatsky
2022-02-15 15:03 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 06/13] printk: refactor and rework printing logic John Ogness
2022-02-16 15:43 ` Petr Mladek
2022-03-02 16:10 ` John Ogness [this message]
2022-02-07 19:43 ` [PATCH printk v1 07/13] printk: move buffer definitions into console_emit_next_record() caller John Ogness
2022-02-16 16:10 ` Petr Mladek
2022-03-02 16:25 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 08/13] printk: add pr_flush() John Ogness
2022-02-17 10:11 ` Petr Mladek
2022-03-02 17:23 ` John Ogness
2022-03-04 13:24 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 09/13] printk: add functions to allow direct printing John Ogness
2022-02-17 12:52 ` Petr Mladek
2022-02-18 9:00 ` David Laight
2022-02-18 12:52 ` Petr Mladek
2022-03-03 14:37 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 10/13] printk: add kthread console printers John Ogness
2022-02-18 9:00 ` early start: was: " Petr Mladek
2022-02-18 9:04 ` start&stop: " Petr Mladek
2022-02-18 9:08 ` main loop: " Petr Mladek
2022-02-18 9:12 ` wake_up_all: " Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 11/13] printk: reimplement console_lock for proper kthread support John Ogness
2022-02-18 16:20 ` Petr Mladek
2022-02-18 21:41 ` John Ogness
2022-02-18 22:03 ` John Ogness
2022-02-22 11:42 ` Petr Mladek
2022-02-23 17:20 ` John Ogness
2022-02-24 8:27 ` Petr Mladek
2022-02-23 10:19 ` Petr Mladek
2022-03-09 13:56 ` John Ogness
2022-03-10 14:34 ` Petr Mladek
2022-03-10 16:08 ` John Ogness
2022-03-11 10:26 ` Petr Mladek
2022-03-11 13:28 ` John Ogness
2022-03-11 16:17 ` Petr Mladek
2022-03-11 22:21 ` John Ogness
2022-03-14 14:08 ` Petr Mladek
2022-03-14 14:43 ` John Ogness
2022-03-14 15:53 ` Petr Mladek
2022-03-11 18:41 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 12/13] printk: remove @console_locked John Ogness
2022-02-23 12:17 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 13/13] console: introduce CON_MIGHT_SLEEP for vt John Ogness
2022-02-23 13:37 ` Petr Mladek
2022-02-23 18:31 ` Greg Kroah-Hartman
[not found] ` <20220208083620.2736-1-hdanton@sina.com>
2022-02-08 11:08 ` [PATCH printk v1 10/13] printk: add kthread console printers John Ogness
2022-02-08 14:53 ` Petr Mladek
2022-02-14 6:12 ` Sergey Senozhatsky
2022-02-14 10:02 ` Petr Mladek
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