On Fri 18-09-15 15:15:36, Andrew Morton wrote:
> On Wed, 19 Aug 2015 17:38:31 +0200 Jan Kara <j...@suse.com> wrote:
>
> > From: Jan Kara <j...@suse.cz>
> >
> > Necessity for offloading of printing was observed only for large
> > systems. So add a config option (disabled by default)
>
> The Kconfig has "default y"?
Changed to 'n'. Thanks for spotting this.
> > which removes most
> > of the overhead added by this functionality.
> >
> > ...
> >
> > +#ifdef CONFIG_PRINTK_OFFLOAD
> > /*
> > * Returns true iff there is other cpu waiting to take over printing. This
> > * function also takes are of setting PRINTK_HANDOVER_B if we want to hand
> > over
> > @@ -2278,6 +2283,14 @@ static bool cpu_stop_printing(int printed_chars)
> >
> > return false;
> > }
> > +#else
> > +
> > +static bool cpu_stop_printing(int printed_chars, bool *woken)
> > +{
> > + return false;
> > +}
> > +
> > +#endif
> >
> > /**
> > * console_unlock - unlock the console system
> > @@ -2316,7 +2329,9 @@ void console_unlock(void)
> > /* flush buffered message fragment immediately to console */
> > console_cont_flush(text, sizeof(text));
> > again:
> > +#ifdef CONFIG_PRINTK_OFFLOAD
> > spin_lock(&print_lock);
> > +#endif
>
> You could nuke a couple of ugly ifdefs by adding
> spin_[un]lock_printk_lock() wrappers into that ifdef/else/endif block
> which holds cpu_stop_printing().
Yup, done.
> > for (;;) {
> > struct printk_log *msg;
> > size_t ext_len = 0;
> > @@ -2399,12 +2414,14 @@ skip:
> >
> > console_locked = 0;
> > up_console_sem();
> > +#ifdef CONFIG_PRINTK_OFFLOAD
> > /*
> > * Release print_lock after console_sem so that printing_task()
> > * succeeds in getting console_sem (unless someone else takes it and
> > * then he'll be responsible for printing).
> > */
> > spin_unlock(&print_lock);
> > +#endif
> >
> > /*
> > * Subtlety: We have interrupts disabled iff hand_over == false (to
> > @@ -2770,6 +2787,7 @@ int unregister_console(struct console *console)
> > }
> > EXPORT_SYMBOL(unregister_console);
> >
> > +#ifdef CONFIG_PRINTK_OFFLOAD
> > /* Kthread which takes over printing from a CPU which asks for help */
> > static int printing_task(void *arg)
> > {
> > @@ -2838,6 +2856,7 @@ static int offload_chars_set(const char *val, const
> > struct kernel_param *kp)
> > mutex_unlock(&printk_kthread_mutex);
> > return 0;
> > }
> > +#endif /* CONFIG_PRINTK_OFFLOAD */
> >
> > static int __init printk_late_init(void)
> > {
> > @@ -2850,9 +2869,11 @@ static int __init printk_late_init(void)
> > }
> > hotcpu_notifier(console_cpu_notify, 0);
> >
> > +#ifdef CONFIG_PRINTK_OFFLOAD
> > mutex_lock(&printk_kthread_mutex);
> > printk_start_offload_kthreads();
> > mutex_unlock(&printk_kthread_mutex);
> > +#endif
>
> Possibly ditto here. Maybe move the mutex_lock() into
> printk_start_offload_kthreads() too?
OK, done.
Honza
--
Jan Kara <j...@suse.com>
SUSE Labs, CR
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