From a32a8813d0173163ba44d8f9556e0d89fdc4fb46 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Fri, 12 Jun 2009 22:27:02 -0600 Subject: 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 --- drivers/lguest/core.c | 7 ++++--- drivers/lguest/hypercalls.c | 4 ++++ drivers/lguest/interrupts_and_traps.c | 16 +++++++++++++--- drivers/lguest/lg.h | 4 ++-- 4 files changed, 23 insertions(+), 8 deletions(-) (limited to 'drivers/lguest') 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 diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c index 54d66f05fefa..f252b71ae79e 100644 --- a/drivers/lguest/hypercalls.c +++ b/drivers/lguest/hypercalls.c @@ -37,6 +37,10 @@ static void do_hcall(struct lg_cpu *cpu, struct hcall_args *args) /* 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 a8c966fee1e4..5a10754b4790 100644 --- a/drivers/lguest/interrupts_and_traps.c +++ b/drivers/lguest/interrupts_and_traps.c @@ -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); } /*:*/ diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h index 6743cf147d97..573896533ac9 100644 --- a/drivers/lguest/lg.h +++ b/drivers/lguest/lg.h @@ -139,8 +139,8 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user); #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); -- cgit v1.2.3-59-g8ed1b