[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v2 1/2] arm/hvf: Optimize and simplify WFI handling
|
From: |
Peter Collingbourne |
|
Subject: |
Re: [PATCH v2 1/2] arm/hvf: Optimize and simplify WFI handling |
|
Date: |
Tue, 1 Dec 2020 17:32:39 -0800 |
On Tue, Dec 1, 2020 at 3:24 PM Alexander Graf <agraf@csgraf.de> wrote:
>
>
> On 01.12.20 22:00, Peter Collingbourne wrote:
> > Sleep on WFx until the VTIMER is due but allow ourselves to be woken
> > up on IPI.
> >
> > Signed-off-by: Peter Collingbourne <pcc@google.com>
> > ---
> > v2:
> > - simplify locking further
> > - wait indefinitely on disabled or masked timers
> >
> > accel/hvf/hvf-cpus.c | 5 +-
> > include/sysemu/hvf_int.h | 3 +-
> > target/arm/hvf/hvf.c | 116 ++++++++++++++-------------------------
> > 3 files changed, 43 insertions(+), 81 deletions(-)
> >
> > diff --git a/accel/hvf/hvf-cpus.c b/accel/hvf/hvf-cpus.c
> > index 4360f64671..b2c8fb57f6 100644
> > --- a/accel/hvf/hvf-cpus.c
> > +++ b/accel/hvf/hvf-cpus.c
> > @@ -344,9 +344,8 @@ static int hvf_init_vcpu(CPUState *cpu)
> > sigact.sa_handler = dummy_signal;
> > sigaction(SIG_IPI, &sigact, NULL);
> >
> > - pthread_sigmask(SIG_BLOCK, NULL, &set);
> > - sigdelset(&set, SIG_IPI);
> > - pthread_sigmask(SIG_SETMASK, &set, NULL);
> > + pthread_sigmask(SIG_BLOCK, NULL, &cpu->hvf->unblock_ipi_mask);
> > + sigdelset(&cpu->hvf->unblock_ipi_mask, SIG_IPI);
> >
> > #ifdef __aarch64__
> > r = hv_vcpu_create(&cpu->hvf->fd, (hv_vcpu_exit_t **)&cpu->hvf->exit,
> > NULL);
> > diff --git a/include/sysemu/hvf_int.h b/include/sysemu/hvf_int.h
> > index c56baa3ae8..13adf6ea77 100644
> > --- a/include/sysemu/hvf_int.h
> > +++ b/include/sysemu/hvf_int.h
> > @@ -62,8 +62,7 @@ extern HVFState *hvf_state;
> > struct hvf_vcpu_state {
> > uint64_t fd;
> > void *exit;
> > - struct timespec ts;
> > - bool sleeping;
> > + sigset_t unblock_ipi_mask;
> > };
> >
> > void assert_hvf_ok(hv_return_t ret);
> > diff --git a/target/arm/hvf/hvf.c b/target/arm/hvf/hvf.c
> > index 8fe10966d2..3321d48aa2 100644
> > --- a/target/arm/hvf/hvf.c
> > +++ b/target/arm/hvf/hvf.c
> > @@ -2,6 +2,7 @@
> > * QEMU Hypervisor.framework support for Apple Silicon
> >
> > * Copyright 2020 Alexander Graf <agraf@csgraf.de>
> > + * Copyright 2020 Google LLC
> > *
> > * This work is licensed under the terms of the GNU GPL, version 2 or
> > later.
> > * See the COPYING file in the top-level directory.
> > @@ -18,6 +19,7 @@
> > #include "sysemu/hw_accel.h"
> >
> > #include <Hypervisor/Hypervisor.h>
> > +#include <mach/mach_time.h>
> >
> > #include "exec/address-spaces.h"
> > #include "hw/irq.h"
> > @@ -320,18 +322,8 @@ int hvf_arch_init_vcpu(CPUState *cpu)
> >
> > void hvf_kick_vcpu_thread(CPUState *cpu)
> > {
> > - if (cpu->hvf->sleeping) {
> > - /*
> > - * When sleeping, make sure we always send signals. Also, clear the
> > - * timespec, so that an IPI that arrives between setting
> > hvf->sleeping
> > - * and the nanosleep syscall still aborts the sleep.
> > - */
> > - cpu->thread_kicked = false;
> > - cpu->hvf->ts = (struct timespec){ };
> > - cpus_kick_thread(cpu);
> > - } else {
> > - hv_vcpus_exit(&cpu->hvf->fd, 1);
> > - }
> > + cpus_kick_thread(cpu);
> > + hv_vcpus_exit(&cpu->hvf->fd, 1);
> > }
> >
> > static int hvf_inject_interrupts(CPUState *cpu)
> > @@ -349,6 +341,18 @@ static int hvf_inject_interrupts(CPUState *cpu)
> > return 0;
> > }
> >
> > +static void hvf_wait_for_ipi(CPUState *cpu, struct timespec *ts)
> > +{
> > + /*
> > + * Use pselect to sleep so that other threads can IPI us while we're
> > + * sleeping.
> > + */
> > + qatomic_mb_set(&cpu->thread_kicked, false);
> > + qemu_mutex_unlock_iothread();
> > + pselect(0, 0, 0, 0, ts, &cpu->hvf->unblock_ipi_mask);
> > + qemu_mutex_lock_iothread();
> > +}
> > +
> > int hvf_vcpu_exec(CPUState *cpu)
> > {
> > ARMCPU *arm_cpu = ARM_CPU(cpu);
> > @@ -357,15 +361,11 @@ int hvf_vcpu_exec(CPUState *cpu)
> > hv_return_t r;
> > int ret = 0;
> >
> > - qemu_mutex_unlock_iothread();
> > -
> > do {
> > bool advance_pc = false;
> >
> > - qemu_mutex_lock_iothread();
> > current_cpu = cpu;
> > qemu_wait_io_event_common(cpu);
> > - qemu_mutex_unlock_iothread();
> >
> > flush_cpu_state(cpu);
> >
> > @@ -374,10 +374,10 @@ int hvf_vcpu_exec(CPUState *cpu)
> > }
> >
> > if (cpu->halted) {
> > - qemu_mutex_lock_iothread();
> > return EXCP_HLT;
> > }
> >
> > + qemu_mutex_unlock_iothread();
> > assert_hvf_ok(hv_vcpu_run(cpu->hvf->fd));
> >
> > /* handle VMEXIT */
> > @@ -385,15 +385,14 @@ int hvf_vcpu_exec(CPUState *cpu)
> > uint64_t syndrome = hvf_exit->exception.syndrome;
> > uint32_t ec = syn_get_ec(syndrome);
> >
> > + qemu_mutex_lock_iothread();
> > switch (exit_reason) {
> > case HV_EXIT_REASON_EXCEPTION:
> > /* This is the main one, handle below. */
> > break;
> > case HV_EXIT_REASON_VTIMER_ACTIVATED:
> > - qemu_mutex_lock_iothread();
> > current_cpu = cpu;
> > qemu_set_irq(arm_cpu->gt_timer_outputs[GTIMER_VIRT], 1);
> > - qemu_mutex_unlock_iothread();
> > continue;
> > case HV_EXIT_REASON_CANCELED:
> > /* we got kicked, no exit to process */
> > @@ -413,7 +412,6 @@ int hvf_vcpu_exec(CPUState *cpu)
> > uint32_t srt = (syndrome >> 16) & 0x1f;
> > uint64_t val = 0;
> >
> > - qemu_mutex_lock_iothread();
> > current_cpu = cpu;
> >
> > DPRINTF("data abort: [pc=0x%llx va=0x%016llx pa=0x%016llx
> > isv=%x "
> > @@ -446,8 +444,6 @@ int hvf_vcpu_exec(CPUState *cpu)
> > hvf_set_reg(cpu, srt, val);
> > }
> >
> > - qemu_mutex_unlock_iothread();
> > -
> > advance_pc = true;
> > break;
> > }
> > @@ -493,68 +489,40 @@ int hvf_vcpu_exec(CPUState *cpu)
> > case EC_WFX_TRAP:
> > if (!(syndrome & WFX_IS_WFE) && !(cpu->interrupt_request &
> > (CPU_INTERRUPT_HARD | CPU_INTERRUPT_FIQ))) {
> > - uint64_t cval, ctl, val, diff, now;
> > + advance_pc = true;
> >
> > - /* Set up a local timer for vtimer if necessary ... */
> > - r = hv_vcpu_get_sys_reg(cpu->hvf->fd,
> > HV_SYS_REG_CNTV_CTL_EL0, &ctl);
> > - assert_hvf_ok(r);
> > - r = hv_vcpu_get_sys_reg(cpu->hvf->fd,
> > HV_SYS_REG_CNTV_CVAL_EL0, &cval);
> > + uint64_t ctl;
> > + r = hv_vcpu_get_sys_reg(cpu->hvf->fd,
> > HV_SYS_REG_CNTV_CTL_EL0,
> > + &ctl);
> > assert_hvf_ok(r);
> >
> > - asm volatile("mrs %0, cntvct_el0" : "=r"(val));
> > - diff = cval - val;
> > -
> > - now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) /
> > - gt_cntfrq_period_ns(arm_cpu);
> > -
> > - /* Timer disabled or masked, just wait for long */
> > if (!(ctl & 1) || (ctl & 2)) {
> > - diff = (120 * NANOSECONDS_PER_SECOND) /
> > - gt_cntfrq_period_ns(arm_cpu);
> > + /* Timer disabled or masked, just wait for an IPI. */
> > + hvf_wait_for_ipi(cpu, NULL);
> > + break;
> > }
> >
> > - if (diff < INT64_MAX) {
> > - uint64_t ns = diff * gt_cntfrq_period_ns(arm_cpu);
> > - struct timespec *ts = &cpu->hvf->ts;
> > -
> > - *ts = (struct timespec){
> > - .tv_sec = ns / NANOSECONDS_PER_SECOND,
> > - .tv_nsec = ns % NANOSECONDS_PER_SECOND,
> > - };
> > -
> > - /*
> > - * Waking up easily takes 1ms, don't go to sleep for
> > smaller
> > - * time periods than 2ms.
> > - */
> > - if (!ts->tv_sec && (ts->tv_nsec < (SCALE_MS * 2))) {
> > - advance_pc = true;
> > - break;
> > - }
> > -
> > - /* Set cpu->hvf->sleeping so that we get a SIG_IPI
> > signal. */
> > - cpu->hvf->sleeping = true;
> > - smp_mb();
> > -
> > - /* Bail out if we received an IRQ meanwhile */
> > - if (cpu->thread_kicked || (cpu->interrupt_request &
> > - (CPU_INTERRUPT_HARD | CPU_INTERRUPT_FIQ))) {
> > - cpu->hvf->sleeping = false;
> > - break;
> > - }
> > -
> > - /* nanosleep returns on signal, so we wake up on kick.
> > */
> > - nanosleep(ts, NULL);
> > -
> > - /* Out of sleep - either naturally or because of a
> > kick */
> > - cpu->hvf->sleeping = false;
> > + uint64_t cval;
> > + r = hv_vcpu_get_sys_reg(cpu->hvf->fd,
> > HV_SYS_REG_CNTV_CVAL_EL0,
> > + &cval);
> > + assert_hvf_ok(r);
> > +
> > + int64_t ticks_to_sleep = cval - mach_absolute_time();
>
>
> I think you touched based on it in a previous thread, but would you mind
> to explain again why mach_absolute_time() is the right thing to check
> cval against? If I read the headers correctly, the cnvt_off register
> should be 0, so cntvct should be the reference time, no?
In my experiments I've found that CNTPCT_EL0 and CNTVCT_EL0 are the
same when read on the host (i.e. host CNTVOFF_EL2 = 0). When we look
at the guest we see that CNTPCT_EL0 corresponds to
mach_absolute_time() on the host and not host CNTPCT_EL0 (if you look
at XNU kernel sources you will see that mach_absolute_time() reads
CNTPCT_EL0 and adds a constant corresponding to the amount of time
that the machine spends asleep) so I think that what's going on at the
hypervisor level is that guest CNTPOFF_EL2 is being set to the same
constant to make it correspond to mach_absolute_time().
> Also, can you please split the patch into one that I can squash into my
> existing one (remove WFI handling altogether), an individual one to
> revive the global io lock (happy to squash too unless you think it's
> useful to keep separate) and then this one?
Sure, I'll do that.
Peter