Messages in this thread | | | Date | Wed, 23 Mar 2016 11:04:20 +0100 | From | Petr Mladek <> | Subject | Re: [RFC][PATCH v6 1/2] printk: Make printk() completely async |
| |
On Wed 2016-03-23 09:37:25, Sergey Senozhatsky wrote: > Hello Petr, > > On (03/22/16 14:11), Petr Mladek wrote: > > > + * Set printing_func() sleep condition early, under the @logbuf_lock. > > > + * So printing kthread (if RUNNING) will go to console_lock() and spin > > > + * on @logbuf_lock. > > > + */ > > > + if (!printk_sync) > > > + need_flush_console = true; > > > > We set this variable for each call and also when printk_kthread is > > NULL or when sync_printk is false. > > hm, yes. (printk_kthread && !need_flush_console) makes more sense. > so we it doesn't get re-dirty if already set.
This does not solve the problem mentioned below. There still might be extra cycle if the kthread is inside console_unclock().
> > We migth want to clear it also from console_unlock(). I think that > > a good place would be in the check: > > > > raw_spin_lock(&logbuf_lock); > > retry = console_seq != log_next_seq; > > raw_spin_unlock_irqrestore(&logbuf_lock, flags); > > hm, what's wrong with clearing it in printk_kthread printing function?
I though about the following scenario:
CPU0 CPU1
vprintk_emit() need_flush_console = true;
wake_up_process(printk_thread)
printing_func()
need_flush_console = false;
console_lock() console_unlock()
vprintk_emit()
need_flush_console = true;
# flush 1st message # flush 2nd message
if (!need_flush_console) # fails and continues
console_lock() console_unlock()
# nope because 2nd # message already flushed
if (!need_flush_console) schedule()
# did one unnecessary # cycle to get asleep
Best Regards, Petr
PS: If you touch the code, please rename printing_func() to printk_kthread_func() to make it more clear what it does. I am sorry for nitpicking.
| |