[PREEMPT_RT]: Using printk-rt-aware.patch in non-rt kernel
From: Pintu Kumar <hidden>
Date: 2018-07-18 14:49:31
Also in:
linux-rt-users, lkml
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 [off-list ref] 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.
quoted hunk
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 <redacted> Date: Wed, 19 Sep 2012 14:50:37 +0200 Subject: [PATCH 224/405] printk-rt-aware.patch Signed-off-by: Thomas Gleixner <redacted> --- 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