Some serial 8250 devices may work with very high speed.
While was using QEMU KVM was observed speed
1..100 Mbit/sec, it fully depends at host machine.
It may affects on responsiveness of system due a cpu
would be spinning in 8250 driver at burst. So added
opportunity to put this processing in kthread.
Signed-off-by: Denys Zagorui <dzagorui@xxxxxxxxx>
---
drivers/tty/serial/8250/8250_core.c | 29 +++++++++++++++++++++++++++++
drivers/tty/serial/8250/8250_port.c | 10 ++++++++++
drivers/tty/serial/8250/Kconfig | 10 ++++++++++
3 files changed, 49 insertions(+)
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 1aab3010fbfa..7b498d2e882b 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -58,7 +58,11 @@ static struct uart_driver serial8250_reg;
static unsigned int skip_txen_test; /* force skip of txen test at init time */
+#ifdef CONFIG_SERIAL_8250_THREADED_IRQ
+#define PASS_LIMIT 32
+#else
#define PASS_LIMIT 512
+#endif
#include <asm/serial.h>
/*
@@ -135,10 +139,16 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
l = l->next;
if (l == i->head && pass_counter++ > PASS_LIMIT) {
+#ifdef CONFIG_SERIAL_8250_THREADED_IRQ
+ cond_resched();
+ pass_counter = 0;
+#else
/* If we hit this, we're dead. */
printk_ratelimited(KERN_ERR
"serial8250: too much work for irq%d\n", irq);
break;
+
+#endif
}
} while (l != end);
@@ -146,9 +156,23 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
pr_debug("%s(%d): end\n", __func__, irq);
+#ifdef CONFIG_SERIAL_8250_THREADED_IRQ
+ enable_irq(i->irq);
+#endif
return IRQ_RETVAL(handled);
}
+#ifdef CONFIG_SERIAL_8250_THREADED_IRQ
+static irqreturn_t serial8250_hard_irq(int irq, void *dev_id)
+{
+ struct irq_info *i = dev_id;
+
+ disable_irq_nosync(i->irq);
+
+ return IRQ_WAKE_THREAD;
+}
+#endif
+
/*
* To support ISA shared interrupts, we need to have one interrupt
* handler that ensures that the IRQ line has been deasserted
@@ -217,8 +241,13 @@ static int serial_link_irq_chain(struct uart_8250_port *up)
i->head = &up->list;
spin_unlock_irq(&i->lock);
irq_flags |= up->port.irqflags;
+#ifdef CONFIG_SERIAL_8250_THREADED_IRQ
+ ret = request_threaded_irq(up->port.irq, serial8250_hard_irq,
+ serial8250_interrupt, irq_flags, up->port.name, i);
+#else
ret = request_irq(up->port.irq, serial8250_interrupt,
irq_flags, up->port.name, i);
+#endif
if (ret < 0)
serial_do_unlink(i, up);
}
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index a5fe0e66c607..16e647473c4d 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1827,13 +1827,19 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir)
int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
{
unsigned char status;
+#ifndef CONFIG_SERIAL_8250_THREADED_IRQ
unsigned long flags;
+#endif
struct uart_8250_port *up = up_to_u8250p(port);
if (iir & UART_IIR_NO_INT)
return 0;
+#ifdef CONFIG_SERIAL_8250_THREADED_IRQ
+ spin_lock(&port->lock);
+#else
spin_lock_irqsave(&port->lock, flags);
+#endif
status = serial_port_in(port, UART_LSR);
@@ -1845,7 +1851,11 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
if ((!up->dma || up->dma->tx_err) && (status & UART_LSR_THRE))
serial8250_tx_chars(up);
+#ifdef CONFIG_SERIAL_8250_THREADED_IRQ
+ spin_unlock(&port->lock);
+#else
spin_unlock_irqrestore(&port->lock, flags);
+#endif
return 1;
}
EXPORT_SYMBOL_GPL(serial8250_handle_irq);
diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
index a1161ec0256f..58a0f324cbea 100644
--- a/drivers/tty/serial/8250/Kconfig
+++ b/drivers/tty/serial/8250/Kconfig
@@ -202,6 +202,16 @@ config SERIAL_8250_MANY_PORTS
say N here to save some memory. You can also say Y if you have an
"intelligent" multiport card such as Cyclades, Digiboards, etc.
+config SERIAL_8250_THREADED_IRQ
+ bool "Make serial 8250 interrupt processing threaded"
+ depends on SERIAL_8250
+ help
+ Some virtual devices can work at very high speed (like QEMU KVM
+ serial 8250). So when burst happens this processing will capture
+ cpu.
+ Say Y if you want to make processing more friendly for others
+ processes.
+
#
# Multi-port serial cards
#
--
2.11.0
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