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@xxxxxxxxxx> > --- > 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); > -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
