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[Qemu-devel] [4335] 8250: throttle TX-completion IRQs
From: |
Aurelien Jarno |
Subject: |
[Qemu-devel] [4335] 8250: throttle TX-completion IRQs |
Date: |
Sun, 04 May 2008 21:42:01 +0000 |
Revision: 4335
http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=4335
Author: aurel32
Date: 2008-05-04 21:42:00 +0000 (Sun, 04 May 2008)
Log Message:
-----------
8250: throttle TX-completion IRQs
(Jan Kiszka)
Modified Paths:
--------------
trunk/hw/serial.c
Modified: trunk/hw/serial.c
===================================================================
--- trunk/hw/serial.c 2008-05-04 20:11:44 UTC (rev 4334)
+++ trunk/hw/serial.c 2008-05-04 21:42:00 UTC (rev 4335)
@@ -25,6 +25,7 @@
#include "qemu-char.h"
#include "isa.h"
#include "pc.h"
+#include "qemu-timer.h"
//#define DEBUG_SERIAL
@@ -73,6 +74,13 @@
#define UART_LSR_OE 0x02 /* Overrun error indicator */
#define UART_LSR_DR 0x01 /* Receiver data ready */
+/*
+ * Delay TX IRQ after sending as much characters as the given interval would
+ * contain on real hardware. This avoids overloading the guest if it processes
+ * its output buffer in a loop inside the TX IRQ handler.
+ */
+#define THROTTLE_TX_INTERVAL 10 /* ms */
+
struct SerialState {
uint16_t divider;
uint8_t rbr; /* receive register */
@@ -91,6 +99,8 @@
int last_break_enable;
target_phys_addr_t base;
int it_shift;
+ QEMUTimer *tx_timer;
+ int tx_burst;
};
static void serial_receive_byte(SerialState *s, int ch);
@@ -111,6 +121,28 @@
}
}
+static void serial_tx_done(void *opaque)
+{
+ SerialState *s = opaque;
+
+ if (s->tx_burst < 0) {
+ uint16_t divider;
+
+ if (s->divider)
+ divider = s->divider;
+ else
+ divider = 1;
+
+ /* We assume 10 bits/char, OK for this purpose. */
+ s->tx_burst = THROTTLE_TX_INTERVAL * 1000 /
+ (1000000 * 10 / (115200 / divider));
+ }
+ s->thr_ipending = 1;
+ s->lsr |= UART_LSR_THRE;
+ s->lsr |= UART_LSR_TEMT;
+ serial_update_irq(s);
+}
+
static void serial_update_parameters(SerialState *s)
{
int speed, parity, data_bits, stop_bits;
@@ -166,15 +198,18 @@
if (!(s->mcr & UART_MCR_LOOP)) {
/* when not in loopback mode, send the char */
qemu_chr_write(s->chr, &ch, 1);
- }
- s->thr_ipending = 1;
- s->lsr |= UART_LSR_THRE;
- s->lsr |= UART_LSR_TEMT;
- serial_update_irq(s);
- if (s->mcr & UART_MCR_LOOP) {
+ } else {
/* in loopback mode, say that we just received a char */
serial_receive_byte(s, ch);
}
+ if (s->tx_burst > 0) {
+ s->tx_burst--;
+ serial_tx_done(s);
+ } else if (s->tx_burst == 0) {
+ s->tx_burst--;
+ qemu_mod_timer(s->tx_timer, qemu_get_clock(vm_clock) +
+ ticks_per_sec * THROTTLE_TX_INTERVAL / 1000);
+ }
}
break;
case 1:
@@ -387,6 +422,10 @@
return NULL;
s->irq = irq;
+ s->tx_timer = qemu_new_timer(vm_clock, serial_tx_done, s);
+ if (!s->tx_timer)
+ return NULL;
+
qemu_register_reset(serial_reset, s);
serial_reset(s);
@@ -486,6 +525,10 @@
s->base = base;
s->it_shift = it_shift;
+ s->tx_timer = qemu_new_timer(vm_clock, serial_tx_done, s);
+ if (!s->tx_timer)
+ return NULL;
+
qemu_register_reset(serial_reset, s);
serial_reset(s);
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