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>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 8ca1def5b142..03fbc88c0023 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -189,6 +189,7 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
         /* 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 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
                 /* 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 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
                         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