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lguest: improve interrupt handling, speed up stream networking

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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>
This commit is contained in:
Rusty Russell
2009-06-12 22:27:02 -06:00
parent abd41f037e
commit a32a8813d0
8 changed files with 43 additions and 16 deletions
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16
drivers/lguest/interrupts_and_traps.c
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@@ -131,7 +131,7 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
* 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 @@ unsigned int interrupt_pending(struct lg_cpu *cpu)
/* 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 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq)
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 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq)
* 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);
}
/*:*/