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/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. */