Messages in this thread | | | Subject | Re: [PATCH] serial: core: prevent softlockups on slow consoles | From | Peter Hurley <> | Date | Wed, 2 Sep 2015 10:38:21 -0400 |
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Hi Vitaly,
On 08/31/2015 10:34 AM, Vitaly Kuznetsov wrote: > Hyper-V serial port is very slow on multi-vCPU guest
How slow and why?
> this causes > soflockups on intensive console writes. Touch nmi watchdog after putting > every char on port to avoid the issue for all serial drivers, the overhead > should be small.
Once per message should be sufficient.
Although I have no objection to adding this to uart_console_write() for all serial drivers, please remove it from drivers that already do this.
> This is just a part of the fix: serial8250_console_write() disables irqs > for all its execution time
Interrupts are disabled by printk()/console_unlock() right now anyway; very thorny problem to fix with lots of complications.
Regards, Peter Hurley
> (which on such slow consoles can be dozens of > seconds), it should be possible to observe devices being stuck on this > CPU. We need to find a better way, e.g. do output in batches enabling irqs > in between. > > Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> > --- > drivers/tty/serial/serial_core.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c > index f368520..cc05785 100644 > --- a/drivers/tty/serial/serial_core.c > +++ b/drivers/tty/serial/serial_core.c > @@ -33,7 +33,7 @@ > #include <linux/serial.h> /* for serial_state and serial_icounter_struct */ > #include <linux/serial_core.h> > #include <linux/delay.h> > -#include <linux/mutex.h>
Why isn't this required anymore?
> +#include <linux/nmi.h> > > #include <asm/irq.h> > #include <asm/uaccess.h> > @@ -1792,6 +1792,7 @@ void uart_console_write(struct uart_port *port, const char *s, > if (*s == '\n') > putchar(port, '\r'); > putchar(port, *s); > + touch_nmi_watchdog(); > } > } > EXPORT_SYMBOL_GPL(uart_console_write); >
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