Hi All, I have a question about PREEMPT_RT patch for 3.10 kernel. I am trying to port this rt patch: 0224-printk-rt-aware.patch.patch (see the patch below), in non-rt kernel. I could able to successfully apply this patch after replacing: migrate_enable/disable with preempt_enable/disable. Things were working fine so far. Then, I noticed that "printk" from interrupt context is not appearing on console (minicom), if console shell is active. However, it appears on the dmesg output. So, I am wondering, what could be the cause of this patch for this behavior in non-rt kernel? Is this the expected behavior, even on PREEMPT_RT kernel? Is there a way we can fix this issue on non-rt kernel? Please help us with your suggestions. Thanks, Pintu On Wed, Jun 13, 2018 at 8:02 PM Pintu Kumar <pintu.ping@xxxxxxxxx> wrote: > > Dear Thomas, > > I was looking into this RT patches for 3.10 kernel: > https://mirrors.edge.kernel.org/pub/linux/kernel/projects/rt/3.10/patches-3.10.108-rt123.tar.gz > > And I came across your patch: 0224-printk-rt-aware.patch.patch > I guess, this patch is related to improving irq latency during printk. > And this patch can work only if PREEMPT_RT_FULL is enabled. > > But, I have 3.10 non-RT kernel, and still I want to use this feature > for non-RT case and achieve the same functionality. > Can you give me some idea, how to convert this RT patch to non-RT > kernel and still achieve the same behavior. > I know this is weird but it is our internal requirement. > > So, if you have any suggestions, it will be really helpful. > > Thank You! > > Regards, > Pintu > > This is the patch details: > ----------------------------------- > rt-patches/patches$ cat 0224-printk-rt-aware.patch.patch > From ec944721d45454681485906615affa9368e0dfae Mon Sep 17 00:00:00 2001 > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Date: Wed, 19 Sep 2012 14:50:37 +0200 > Subject: [PATCH 224/405] printk-rt-aware.patch > > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > --- > kernel/printk.c | 34 +++++++++++++++++++++++++++++----- > 1 file changed, 29 insertions(+), 5 deletions(-) > > diff --git a/kernel/printk.c b/kernel/printk.c > index e879b8615a0f..07d32a2c8a5f 100644 > --- a/kernel/printk.c > +++ b/kernel/printk.c > @@ -1277,6 +1277,7 @@ static void call_console_drivers(int level, > const char *text, size_t len) > if (!console_drivers) > return; > > + migrate_disable(); > for_each_console(con) { > if (exclusive_console && con != exclusive_console) > continue; > @@ -1289,6 +1290,7 @@ static void call_console_drivers(int level, > const char *text, size_t len) > continue; > con->write(con, text, len); > } > + migrate_enable(); > } > > /* > @@ -1348,12 +1350,18 @@ static inline int can_use_console(unsigned int cpu) > * interrupts disabled. It should return with 'lockbuf_lock' > * released but interrupts still disabled. > */ > -static int console_trylock_for_printk(unsigned int cpu) > +static int console_trylock_for_printk(unsigned int cpu, unsigned long flags) > __releases(&logbuf_lock) > { > int retval = 0, wake = 0; > +#ifdef CONFIG_PREEMPT_RT_FULL > + int lock = !early_boot_irqs_disabled && !irqs_disabled_flags(flags) && > + (preempt_count() <= 1); > +#else > + int lock = 1; > +#endif > > - if (console_trylock()) { > + if (lock && console_trylock()) { > retval = 1; > > /* > @@ -1688,8 +1696,15 @@ asmlinkage int vprintk_emit(int facility, int level, > * The console_trylock_for_printk() function will release 'logbuf_lock' > * regardless of whether it actually gets the console semaphore or not. > */ > - if (console_trylock_for_printk(this_cpu)) > + if (console_trylock_for_printk(this_cpu, flags)) { > +#ifndef CONFIG_PREEMPT_RT_FULL > console_unlock(); > +#else > + raw_local_irq_restore(flags); > + console_unlock(); > + raw_local_irq_save(flags); > +#endif > + } > > lockdep_on(); > out_restore_irqs: > @@ -2043,11 +2058,16 @@ static void console_cont_flush(char *text, size_t size) > goto out; > > len = cont_print_text(text, size); > +#ifndef CONFIG_PREEMPT_RT_FULL > raw_spin_unlock(&logbuf_lock); > stop_critical_timings(); > call_console_drivers(cont.level, text, len); > start_critical_timings(); > local_irq_restore(flags); > +#else > + raw_spin_unlock_irqrestore(&logbuf_lock, flags); > + call_console_drivers(cont.level, text, len); > +#endif > return; > out: > raw_spin_unlock_irqrestore(&logbuf_lock, flags); > @@ -2141,13 +2161,17 @@ skip: > console_idx = log_next(console_idx); > console_seq++; > console_prev = msg->flags; > - raw_spin_unlock(&logbuf_lock); > > +#ifndef CONFIG_PREEMPT_RT_FULL > + raw_spin_unlock(&logbuf_lock); > stop_critical_timings(); /* don't trace print latency */ > call_console_drivers(level, text, len); > start_critical_timings(); > local_irq_restore(flags); > - > +#else > + raw_spin_unlock_irqrestore(&logbuf_lock, flags); > + call_console_drivers(level, text, len); > +#endif > if (do_cond_resched) > cond_resched(); > } > -- > 2.13.2 -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
