From: John Ogness <john.ogness@linutronix.de>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andrea Parri <andrea.parri@amarulasolutions.com>,
Thomas Gleixner <tglx@linutronix.de>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer implementation
Date: Tue, 25 Jun 2019 10:44:19 +0200 [thread overview]
Message-ID: <875zoujbq4.fsf@linutronix.de> (raw)
In-Reply-To: <20190625071500.GB19050@jagdpanzerIV> (Sergey Senozhatsky's message of "Tue, 25 Jun 2019 16:15:00 +0900")
On 2019-06-25, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote:
>>>> + struct prb_reserved_entry e;
>>>> + char *s;
>>>> +
>>>> + s = prb_reserve(&e, &rb, 32);
>>>> + if (s) {
>>>> + sprintf(s, "Hello, world!");
>>>> + prb_commit(&e);
>>>> + }
>>>
>>> A nit: snprintf().
>>>
>>> sprintf() is tricky, it may write "slightly more than was
>>> anticipated" bytes - all those string_nocheck(" disabled"),
>>> error_string("pK-error"), etc.
>>
>> Agreed. Documentation should show good examples.
>
> In vprintk_emit(), are we going to always reserve 1024-byte
> records, since we don't know the size in advance, e.g.
>
> printk("%pS %s\n", regs->ip, current->name)
> prb_reserve(&e, &rb, ????);
>
> or are we going to run vscnprintf() on a NULL buffer first,
> then reserve the exactly required number of bytes and afterwards
> vscnprintf(s) -> prb_commit(&e)?
(As suggested by Petr) I want to use vscnprintf() on a NULL
buffer. However, a NULL buffer is not sufficient because things like the
loglevel are sometimes added via %s (for example, in /dev/kmsg). So
rather than a NULL buffer, I would use a small buffer on the stack
(large enough to store loglevel/cont information). This way we can use
vscnprintf() to get the exact size _and_ printk_get_level() will see
enough of the formatted string to parse what it needs.
> I'm asking this because, well, if the most common usage
> pattern (printk->prb_reserve) will always reserve fixed
> size records (aka data blocks), then you _probably_ (??)
> can drop the 'variable size records' requirement from prb
> design and start looking at records (aka data blocks) as
> fixed sized chunks of bytes, which are always located at
> fixed offsets.
The average printk message size is well under 128 bytes. It would be
quite wasteful to always reserve 1K blocks.
John Ogness
next prev parent reply other threads:[~2019-06-25 8:45 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-07 16:23 [RFC PATCH v2 0/2] printk: new ringbuffer implementation John Ogness
2019-06-07 16:23 ` [RFC PATCH v2 1/2] printk-rb: add a new printk " John Ogness
2019-06-18 4:51 ` Sergey Senozhatsky
2019-06-18 22:12 ` John Ogness
2019-06-25 6:45 ` Sergey Senozhatsky
2019-06-25 7:15 ` Sergey Senozhatsky
2019-06-25 8:44 ` John Ogness [this message]
2019-06-25 9:06 ` Petr Mladek
2019-06-25 10:03 ` Sergey Senozhatsky
2019-06-25 12:03 ` John Ogness
2019-06-26 2:08 ` Sergey Senozhatsky
2019-06-26 7:16 ` John Ogness
2019-06-26 7:45 ` Sergey Senozhatsky
2019-06-26 7:47 ` Petr Mladek
2019-06-26 7:59 ` Sergey Senozhatsky
2019-06-25 9:09 ` Sergey Senozhatsky
2019-06-18 11:12 ` Peter Zijlstra
2019-06-18 22:18 ` John Ogness
2019-06-18 11:22 ` Peter Zijlstra
2019-06-18 22:30 ` John Ogness
2019-06-19 10:46 ` Andrea Parri
2019-06-20 22:50 ` John Ogness
2019-06-21 12:16 ` Andrea Parri
2019-06-19 11:08 ` Peter Zijlstra
2019-06-18 11:47 ` Peter Zijlstra
2019-06-20 22:23 ` John Ogness
2019-06-26 22:40 ` Peter Zijlstra
2019-06-26 22:53 ` Peter Zijlstra
2019-06-28 9:50 ` John Ogness
2019-06-28 15:44 ` Peter Zijlstra
2019-06-28 16:07 ` Peter Zijlstra
2019-07-01 10:39 ` John Ogness
2019-07-01 14:10 ` Peter Zijlstra
2019-07-01 14:11 ` Peter Zijlstra
2019-06-29 21:05 ` Andrea Parri
2019-06-30 2:03 ` John Ogness
2019-06-30 14:08 ` Andrea Parri
2019-07-02 14:13 ` John Ogness
2019-06-26 22:47 ` Peter Zijlstra
2019-06-21 14:05 ` Petr Mladek
2019-06-24 8:33 ` John Ogness
2019-06-24 14:09 ` Petr Mladek
2019-06-25 13:29 ` John Ogness
2019-06-26 8:29 ` Petr Mladek
2019-06-26 9:09 ` John Ogness
2019-06-26 21:16 ` Peter Zijlstra
2019-06-26 21:43 ` John Ogness
2019-06-27 8:28 ` Petr Mladek
2019-07-04 10:33 ` [PATCH POC] printk_ringbuffer: Alternative implementation of lockless printk ringbuffer Petr Mladek
2019-07-04 14:59 ` John Ogness
2019-07-08 15:23 ` Petr Mladek
2019-07-09 1:34 ` John Ogness
2019-07-09 9:06 ` Petr Mladek
2019-07-09 10:21 ` John Ogness
2019-07-09 11:58 ` Petr Mladek
2019-08-14 3:46 ` John Ogness
2019-06-24 13:55 ` [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer implementation John Ogness
2019-06-25 8:55 ` Sergey Senozhatsky
2019-06-25 9:19 ` John Ogness
2019-06-07 16:23 ` [RFC PATCH v2 2/2] printk-rb: add test module John Ogness
2019-06-17 21:09 ` [RFC PATCH v2 0/2] printk: new ringbuffer implementation Thomas Gleixner
2019-06-18 7:15 ` Petr Mladek
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