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/arch/x86/include/asm/lguest_hcall.h b/arch/x86/include/asm/lguest_hcall.h
index faae199..f9a9f78 100644
--- a/arch/x86/include/asm/lguest_hcall.h
+++ b/arch/x86/include/asm/lguest_hcall.h
@@ -17,6 +17,7 @@
#define LHCALL_LOAD_TLS 16
#define LHCALL_NOTIFY 17
#define LHCALL_LOAD_GDT_ENTRY 18
+#define LHCALL_SEND_INTERRUPTS 19
#define LGUEST_TRAP_ENTRY 0x1F
diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 2392a7a1..37b8c1d 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -205,6 +205,12 @@
static void restore_fl(unsigned long flags)
{
lguest_data.irq_enabled = flags;
+ mb();
+ /* Null hcall forces interrupt delivery now, if irq_pending is
+ * set to X86_EFLAGS_IF (ie. an interrupt is pending, and flags
+ * enables interrupts. */
+ if (flags & lguest_data.irq_pending)
+ kvm_hypercall0(LHCALL_SEND_INTERRUPTS);
}
PV_CALLEE_SAVE_REGS_THUNK(restore_fl);
@@ -219,6 +225,11 @@
static void irq_enable(void)
{
lguest_data.irq_enabled = X86_EFLAGS_IF;
+ mb();
+ /* Null hcall forces interrupt delivery now. */
+ if (lguest_data.irq_pending)
+ kvm_hypercall0(LHCALL_SEND_INTERRUPTS);
+
}
PV_CALLEE_SAVE_REGS_THUNK(irq_enable);
@@ -972,10 +983,10 @@
*
* Our current solution is to allow the paravirt back end to optionally patch
* over the indirect calls to replace them with something more efficient. We
- * patch the four most commonly called functions: disable interrupts, enable
- * interrupts, restore interrupts and save interrupts. We usually have 6 or 10
- * bytes to patch into: the Guest versions of these operations are small enough
- * that we can fit comfortably.
+ * patch two of the simplest of the most commonly called functions: disable
+ * interrupts and save interrupts. We usually have 6 or 10 bytes to patch
+ * into: the Guest versions of these operations are small enough that we can
+ * fit comfortably.
*
* First we need assembly templates of each of the patchable Guest operations,
* and these are in i386_head.S. */
@@ -986,8 +997,6 @@
const char *start, *end;
} lguest_insns[] = {
[PARAVIRT_PATCH(pv_irq_ops.irq_disable)] = { lgstart_cli, lgend_cli },
- [PARAVIRT_PATCH(pv_irq_ops.irq_enable)] = { lgstart_sti, lgend_sti },
- [PARAVIRT_PATCH(pv_irq_ops.restore_fl)] = { lgstart_popf, lgend_popf },
[PARAVIRT_PATCH(pv_irq_ops.save_fl)] = { lgstart_pushf, lgend_pushf },
};
diff --git a/arch/x86/lguest/i386_head.S b/arch/x86/lguest/i386_head.S
index f795419..3e0c554 100644
--- a/arch/x86/lguest/i386_head.S
+++ b/arch/x86/lguest/i386_head.S
@@ -46,8 +46,6 @@
.globl lgstart_##name; .globl lgend_##name
LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled)
-LGUEST_PATCH(sti, movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled)
-LGUEST_PATCH(popf, movl %eax, lguest_data+LGUEST_DATA_irq_enabled)
LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax)
/*:*/
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 6743cf1..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);
diff --git a/include/linux/lguest.h b/include/linux/lguest.h
index 175e63f..7bc1440 100644
--- a/include/linux/lguest.h
+++ b/include/linux/lguest.h
@@ -30,6 +30,10 @@
/* Wallclock time set by the Host. */
struct timespec time;
+ /* Interrupt pending set by the Host. The Guest should do a hypercall
+ * if it re-enables interrupts and sees this set (to X86_EFLAGS_IF). */
+ int irq_pending;
+
/* Async hypercall ring. Instead of directly making hypercalls, we can
* place them in here for processing the next time the Host wants.
* This batching can be quite efficient. */