lguest: improve interrupt handling, speed up stream networking
lguest never checked for pending interrupts when enabling interrupts, and
things still worked. However, it makes a significant difference to TCP
performance, so it's time we fixed it by introducing a pending_irq flag
and checking it on irq_restore and irq_enable.
These two routines are now too big to patch into the 8/10 bytes
patch space, so we drop that code.
Note: The high latency on interrupt delivery had a very curious
effect: once everything else was optimized, networking without GSO was
faster than networking with GSO, since more interrupts were sent and
hence a greater chance of one getting through to the Guest!
Note2: (Almost) Closing the same loophole for iret doesn't have any
measurable effect, so I'm leaving that patch for the moment.
Before:
1GB tcpblast Guest->Host: 30.7 seconds
1GB tcpblast Guest->Host (no GSO): 76.0 seconds
After:
1GB tcpblast Guest->Host: 6.8 seconds
1GB tcpblast Guest->Host (no GSO): 27.8 seconds
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 8ca1def..03fbc88 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -189,6 +189,7 @@
/* We stop running once the Guest is dead. */
while (!cpu->lg->dead) {
unsigned int irq;
+ bool more;
/* First we run any hypercalls the Guest wants done. */
if (cpu->hcall)
@@ -213,9 +214,9 @@
/* Check if there are any interrupts which can be delivered now:
* if so, this sets up the hander to be executed when we next
* run the Guest. */
- irq = interrupt_pending(cpu);
+ irq = interrupt_pending(cpu, &more);
if (irq < LGUEST_IRQS)
- try_deliver_interrupt(cpu, irq);
+ try_deliver_interrupt(cpu, irq, more);
/* All long-lived kernel loops need to check with this horrible
* thing called the freezer. If the Host is trying to suspend,
@@ -233,7 +234,7 @@
set_current_state(TASK_INTERRUPTIBLE);
/* Just before we sleep, make sure nothing snuck in
* which we should be doing. */
- if (interrupt_pending(cpu) < LGUEST_IRQS
+ if (interrupt_pending(cpu, &more) < LGUEST_IRQS
|| cpu->break_out)
set_current_state(TASK_RUNNING);
else
diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c
index 54d66f0..f252b71 100644
--- a/drivers/lguest/hypercalls.c
+++ b/drivers/lguest/hypercalls.c
@@ -37,6 +37,10 @@
/* This call does nothing, except by breaking out of the Guest
* it makes us process all the asynchronous hypercalls. */
break;
+ case LHCALL_SEND_INTERRUPTS:
+ /* This call does nothing too, but by breaking out of the Guest
+ * it makes us process any pending interrupts. */
+ break;
case LHCALL_LGUEST_INIT:
/* You can't get here unless you're already initialized. Don't
* do that. */
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index a8c966f..5a10754 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -131,7 +131,7 @@
* interrupt_pending() returns the first pending interrupt which isn't blocked
* by the Guest. It is called before every entry to the Guest, and just before
* we go to sleep when the Guest has halted itself. */
-unsigned int interrupt_pending(struct lg_cpu *cpu)
+unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more)
{
unsigned int irq;
DECLARE_BITMAP(blk, LGUEST_IRQS);
@@ -149,13 +149,14 @@
/* Find the first interrupt. */
irq = find_first_bit(blk, LGUEST_IRQS);
+ *more = find_next_bit(blk, LGUEST_IRQS, irq+1);
return irq;
}
/* This actually diverts the Guest to running an interrupt handler, once an
* interrupt has been identified by interrupt_pending(). */
-void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq)
+void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
{
struct desc_struct *idt;
@@ -178,8 +179,12 @@
u32 irq_enabled;
if (get_user(irq_enabled, &cpu->lg->lguest_data->irq_enabled))
irq_enabled = 0;
- if (!irq_enabled)
+ if (!irq_enabled) {
+ /* Make sure they know an IRQ is pending. */
+ put_user(X86_EFLAGS_IF,
+ &cpu->lg->lguest_data->irq_pending);
return;
+ }
}
/* Look at the IDT entry the Guest gave us for this interrupt. The
@@ -202,6 +207,11 @@
* here is a compromise which means at least it gets updated every
* timer interrupt. */
write_timestamp(cpu);
+
+ /* If there are no other interrupts we want to deliver, clear
+ * the pending flag. */
+ if (!more)
+ put_user(0, &cpu->lg->lguest_data->irq_pending);
}
/*:*/
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 6743cf14..573896533 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -139,8 +139,8 @@
#define pgd_pfn(x) (pgd_val(x) >> PAGE_SHIFT)
/* interrupts_and_traps.c: */
-unsigned int interrupt_pending(struct lg_cpu *cpu);
-void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq);
+unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more);
+void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more);
bool deliver_trap(struct lg_cpu *cpu, unsigned int num);
void load_guest_idt_entry(struct lg_cpu *cpu, unsigned int i,
u32 low, u32 hi);
