* Re: printk considered harmful (was: [TECH TOPIC] asynchronous printk)
[not found] <1478106396.23018.51.camel@perches.com>
@ 2016-11-03 17:31 ` Sergey Senozhatsky
2016-11-03 18:01 ` Sergey Senozhatsky
0 siblings, 1 reply; 4+ messages in thread
From: Sergey Senozhatsky @ 2016-11-03 17:31 UTC (permalink / raw)
To: Joe Perches
Cc: Sergey Senozhatsky, Jiri Kosina, Theodore Tso, Hannes Reinecke,
Jan Kara, Petr Mladek, linux-kernel
[Cc linux-kernel]
Hello,
On (11/02/16 10:06), Joe Perches wrote:
> Hello all.
>
> Can you please post notes for whatever is proposed here somewhere?
we covered 4 topics:
#1 deadlocks and recursion in printk
discussion outcome:
I published an updated printk_safe patch last week (addresses recursion
problems in printk). there was no strong opposition, and we agreed
that per-cpu buffers can help us out.
discussion outcome:
we agreed that deadlocks in printk must be addressed via printk
indirection. basically printk() will behave the same way as
printk_deferred() and, thus, we can, at some point, remove
printk_deferred().
#2 async printk
discussion outcome:
we agreed to offload printing duty to a special printk kthread.
#3 pr_cont
discussion outcome:
out of "problems" list. no work will be done in this area.
#4 console semaphore
discussion outcome:
we agreed that we can do better here and that it makes sense to do
what's been proposed in my slides. but, I keep it as a low priority.
frankly. I'd be happy to see #1-#3 in the mainline in 9-12 months.
not because it's such an enormesoly hard thing to do, but because we
probably would want to introduce those changes iteratively, in
different releases.
p.s.
I uploaded "some sort" of slides to
http://www.slideshare.net/SergeySENOZHATSKY/printk-considered-harmful
-ss
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: printk considered harmful (was: [TECH TOPIC] asynchronous printk)
2016-11-03 17:31 ` printk considered harmful (was: [TECH TOPIC] asynchronous printk) Sergey Senozhatsky
@ 2016-11-03 18:01 ` Sergey Senozhatsky
2016-11-03 23:28 ` Jan Kara
0 siblings, 1 reply; 4+ messages in thread
From: Sergey Senozhatsky @ 2016-11-03 18:01 UTC (permalink / raw)
To: Sergey Senozhatsky
Cc: Joe Perches, Jiri Kosina, Theodore Tso, Hannes Reinecke,
Jan Kara, Petr Mladek, linux-kernel
fix a typo
On (11/04/16 02:31), Sergey Senozhatsky wrote:
[..]
> #4 console semaphore
> discussion outcome:
> we agreed that we can do better here and that it makes sense to do
^^^^ IOW, console semaphore thing
can be improved
> what's been proposed in my slides. but, I keep it as a low priority.
> frankly. I'd be happy to see #1-#3 in the mainline in 9-12 months.
^^^^ #1-#2, of course. but #1 consists
of 2 steps.
I'm still not entirely sure if I want to split async pintk and printk
deadlock rework. these things want to come together, for a number of
reasons. or, at least, push the async printk before printk deadlock
rework.
-ss
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: printk considered harmful (was: [TECH TOPIC] asynchronous printk)
2016-11-03 18:01 ` Sergey Senozhatsky
@ 2016-11-03 23:28 ` Jan Kara
2016-11-04 16:07 ` Sergey Senozhatsky
0 siblings, 1 reply; 4+ messages in thread
From: Jan Kara @ 2016-11-03 23:28 UTC (permalink / raw)
To: Sergey Senozhatsky
Cc: Joe Perches, Jiri Kosina, Theodore Tso, Hannes Reinecke,
Jan Kara, Petr Mladek, linux-kernel
On Fri 04-11-16 03:01:31, Sergey Senozhatsky wrote:
> fix a typo
>
> On (11/04/16 02:31), Sergey Senozhatsky wrote:
> [..]
> > #4 console semaphore
> > discussion outcome:
> > we agreed that we can do better here and that it makes sense to do
> ^^^^ IOW, console semaphore thing
> can be improved
>
> > what's been proposed in my slides. but, I keep it as a low priority.
> > frankly. I'd be happy to see #1-#3 in the mainline in 9-12 months.
> ^^^^ #1-#2, of course. but #1 consists
> of 2 steps.
>
> I'm still not entirely sure if I want to split async pintk and printk
> deadlock rework. these things want to come together, for a number of
> reasons. or, at least, push the async printk before printk deadlock
> rework.
Yep, please push async printk patches soon. IMHO there's no reason to wait
with that. You can create a git tree with printk patches and push it directly
to Linus since he seems to be fine with the approach...
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: printk considered harmful (was: [TECH TOPIC] asynchronous printk)
2016-11-03 23:28 ` Jan Kara
@ 2016-11-04 16:07 ` Sergey Senozhatsky
0 siblings, 0 replies; 4+ messages in thread
From: Sergey Senozhatsky @ 2016-11-04 16:07 UTC (permalink / raw)
To: Jan Kara
Cc: Sergey Senozhatsky, Joe Perches, Jiri Kosina, Theodore Tso,
Hannes Reinecke, Jan Kara, Petr Mladek, linux-kernel
Hi Jan,
On (11/04/16 00:28), Jan Kara wrote:
[..]
> > I'm still not entirely sure if I want to split async pintk and printk
> > deadlock rework. these things want to come together, for a number of
> > reasons. or, at least, push the async printk before printk deadlock
> > rework.
>
> Yep, please push async printk patches soon. IMHO there's no reason to wait
> with that. You can create a git tree with printk patches and push it directly
> to Linus since he seems to be fine with the approach...
I'll merge async printk and printk_deferred() patches in one patch set
and then push it (it's just one extra patch in the series; besides we touch
wake_up_klogd_work_func() in async printk anyway), since they really want to
come together. and before async+deferred work I want to push printk_safe. we
already have a somewhat bad experience with printk recursion in async printk,
so I want to stay on the safe side this time.
and, yes, I had this idea of having a printk tree somewhere on github,
so people can start playing with it.
thanks.
-ss
^ permalink raw reply [flat|nested] 4+ messages in thread
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2016-11-03 17:31 ` printk considered harmful (was: [TECH TOPIC] asynchronous printk) Sergey Senozhatsky
2016-11-03 18:01 ` Sergey Senozhatsky
2016-11-03 23:28 ` Jan Kara
2016-11-04 16:07 ` Sergey Senozhatsky
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