From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
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 18:09:34 +0900 [thread overview]
Message-ID: <20190625090934.GC532@jagdpanzerIV> (raw)
In-Reply-To: <875zoujbq4.fsf@linutronix.de>
On (06/25/19 10:44), John Ogness wrote:
> > 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.
OK. I guess this should work except for the cases when we want to
printk that we are running out of stack :)
More seriously, tho, sometimes messages come with dictionaries of
key/value pairs. I don't think we impose any strict limits on the
number of key/value pair or on the overall size of the dictionary
each record can have (up to a single PAGE, I'd guess. I really need
to check printk code). Finding a sufficiently large buffer size
might be a bit of a task.
> > 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.
Do you also count in dictionary of properties (key/value pairs) which
records can carry?
For printks from core kernel 128 bytes would be a good estimation,
for dev_printk() and so on - I'm not exactly sure.
cat /dev/kmsg
This one, for instance, is a single logbuf record
6,560,2470340,-;hid-generic 0003:093A:2510.0001: input,hidraw0: USB HID v1.11 Mouse [PixArt USB Optical Mouse] on usb-0000:00:14.0-3/input0
SUBSYSTEM=hid
DEVICE=+hid:0003:093A:2510.0001
I suspect that it's larger than 128 bytes.
> It would be quite wasteful to always reserve 1K blocks.
Agreed.
-ss
next prev parent reply other threads:[~2019-06-25 9:09 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
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 [this message]
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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