Messages in this thread | | | Date | Tue, 16 Sep 2014 23:22:50 +0200 | From | Jan Kara <> | Subject | Re: [PATCH] printk: git rid of [sched_delayed] message for printk_deferred |
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On Tue 16-09-14 17:07:09, Steven Rostedt wrote: > On Tue, 16 Sep 2014 22:35:10 +0200 > Jan Kara <jack@suse.cz> wrote: > > > On Tue 16-09-14 11:13:31, Steven Rostedt wrote: > > > On Tue, 16 Sep 2014 16:42:52 +0200 > > > Markus Trippelsdorf <markus@trippelsdorf.de> wrote: > > > > > > > commit 458df9fd hardcodes printk_deferred() to KERN_WARNING and inserts > > > > the string "[sched_delayed] " before the actual message. > > > > However it doesn't take into account the KERN_* prefix of the message, > > > > that now ends up in the middle of the output: > > > > > > > > [sched_delayed] ^a4CE: hpet increased min_delta_ns to 20115 nsec > > > > > > > > Fix this by just getting rid of the "[sched_delayed] " scnprintf(). > > > > > > I prefer the "[sched_delayed]" output. It lets us know that the output > > > did not come out immediately, which is important sometimes during > > > debugging. Otherwise it can confuse people, as printk is suppose to be > > > a blocking write. > > This is a common misconception about printk. It isn't a blocking write > > for ten years or more. If there happens to be someone else printing to > > console, the difference between printk() and printk_deferred() is > > marginal - it used to be bigger when scheduler had its own buffer but these > > days message is inserted in the kernel ring buffer immediately. That's why > > I don't think the prefix is useful anymore. > > For the most part it's a blocking write. Yeah, if another CPU is > writing, it wont be a blocking write, but it usually is, I know I > depend on it (when I'm debugging, I usually don't have contention > between CPUs). The important part is that they are done in order. A > delayed print, wont be in order with other printks. That is still a > crucial difference. printk_deffered() will be in order with other printks after your commit 458df9fd4815b47809875d57f42e16401674b621. Just printing to console itself will be delayed to the next timer interrupt. Or am I missing something?
Honza
-- Jan Kara <jack@suse.cz> SUSE Labs, CR
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