qemu

icount.c (16257B)

---

 /*
  * QEMU System Emulator
  *
  * Copyright (c) 2003-2008 Fabrice Bellard
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
 
 #include "qemu/osdep.h"
 #include "qemu/cutils.h"
 #include "migration/vmstate.h"
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "exec/exec-all.h"
 #include "sysemu/cpus.h"
 #include "sysemu/qtest.h"
 #include "qemu/main-loop.h"
 #include "qemu/option.h"
 #include "qemu/seqlock.h"
 #include "sysemu/replay.h"
 #include "sysemu/runstate.h"
 #include "hw/core/cpu.h"
 #include "sysemu/cpu-timers.h"
 #include "sysemu/cpu-throttle.h"
 #include "timers-state.h"
 
 /*
  * ICOUNT: Instruction Counter
  *
  * this module is split off from cpu-timers because the icount part
  * is TCG-specific, and does not need to be built for other accels.
  */
 static bool icount_sleep = true;
 /* Arbitrarily pick 1MIPS as the minimum allowable speed.  */
 #define MAX_ICOUNT_SHIFT 10
 
 /*
  * 0 = Do not count executed instructions.
  * 1 = Fixed conversion of insn to ns via "shift" option
  * 2 = Runtime adaptive algorithm to compute shift
  */
 int use_icount;
 
 static void icount_enable_precise(void)
 {
     use_icount = 1;
 }
 
 static void icount_enable_adaptive(void)
 {
     use_icount = 2;
 }
 
 /*
  * The current number of executed instructions is based on what we
  * originally budgeted minus the current state of the decrementing
  * icount counters in extra/u16.low.
  */
 static int64_t icount_get_executed(CPUState *cpu)
 {
     return (cpu->icount_budget -
             (cpu_neg(cpu)->icount_decr.u16.low + cpu->icount_extra));
 }
 
 /*
  * Update the global shared timer_state.qemu_icount to take into
  * account executed instructions. This is done by the TCG vCPU
  * thread so the main-loop can see time has moved forward.
  */
 static void icount_update_locked(CPUState *cpu)
 {
     int64_t executed = icount_get_executed(cpu);
     cpu->icount_budget -= executed;
 
     qatomic_set_i64(&timers_state.qemu_icount,
                     timers_state.qemu_icount + executed);
 }
 
 /*
  * Update the global shared timer_state.qemu_icount to take into
  * account executed instructions. This is done by the TCG vCPU
  * thread so the main-loop can see time has moved forward.
  */
 void icount_update(CPUState *cpu)
 {
     seqlock_write_lock(&timers_state.vm_clock_seqlock,
                        &timers_state.vm_clock_lock);
     icount_update_locked(cpu);
     seqlock_write_unlock(&timers_state.vm_clock_seqlock,
                          &timers_state.vm_clock_lock);
 }
 
 static int64_t icount_get_raw_locked(void)
 {
     CPUState *cpu = current_cpu;
 
     if (cpu && cpu->running) {
         if (!cpu->can_do_io) {
             error_report("Bad icount read");
             exit(1);
         }
         /* Take into account what has run */
         icount_update_locked(cpu);
     }
     /* The read is protected by the seqlock, but needs atomic64 to avoid UB */
     return qatomic_read_i64(&timers_state.qemu_icount);
 }
 
 static int64_t icount_get_locked(void)
 {
     int64_t icount = icount_get_raw_locked();
     return qatomic_read_i64(&timers_state.qemu_icount_bias) +
         icount_to_ns(icount);
 }
 
 int64_t icount_get_raw(void)
 {
     int64_t icount;
     unsigned start;
 
     do {
         start = seqlock_read_begin(&timers_state.vm_clock_seqlock);
         icount = icount_get_raw_locked();
     } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, start));
 
     return icount;
 }
 
 /* Return the virtual CPU time, based on the instruction counter.  */
 int64_t icount_get(void)
 {
     int64_t icount;
     unsigned start;
 
     do {
         start = seqlock_read_begin(&timers_state.vm_clock_seqlock);
         icount = icount_get_locked();
     } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, start));
 
     return icount;
 }
 
 int64_t icount_to_ns(int64_t icount)
 {
     return icount << qatomic_read(&timers_state.icount_time_shift);
 }
 
 /*
  * Correlation between real and virtual time is always going to be
  * fairly approximate, so ignore small variation.
  * When the guest is idle real and virtual time will be aligned in
  * the IO wait loop.
  */
 #define ICOUNT_WOBBLE (NANOSECONDS_PER_SECOND / 10)
 
 static void icount_adjust(void)
 {
     int64_t cur_time;
     int64_t cur_icount;
     int64_t delta;
 
     /* If the VM is not running, then do nothing.  */
     if (!runstate_is_running()) {
         return;
     }
 
     seqlock_write_lock(&timers_state.vm_clock_seqlock,
                        &timers_state.vm_clock_lock);
     cur_time = REPLAY_CLOCK_LOCKED(REPLAY_CLOCK_VIRTUAL_RT,
                                    cpu_get_clock_locked());
     cur_icount = icount_get_locked();
 
     delta = cur_icount - cur_time;
     /* FIXME: This is a very crude algorithm, somewhat prone to oscillation.  */
     if (delta > 0
         && timers_state.last_delta + ICOUNT_WOBBLE < delta * 2
         && timers_state.icount_time_shift > 0) {
         /* The guest is getting too far ahead.  Slow time down.  */
         qatomic_set(&timers_state.icount_time_shift,
                     timers_state.icount_time_shift - 1);
     }
     if (delta < 0
         && timers_state.last_delta - ICOUNT_WOBBLE > delta * 2
         && timers_state.icount_time_shift < MAX_ICOUNT_SHIFT) {
         /* The guest is getting too far behind.  Speed time up.  */
         qatomic_set(&timers_state.icount_time_shift,
                     timers_state.icount_time_shift + 1);
     }
     timers_state.last_delta = delta;
     qatomic_set_i64(&timers_state.qemu_icount_bias,
                     cur_icount - (timers_state.qemu_icount
                                   << timers_state.icount_time_shift));
     seqlock_write_unlock(&timers_state.vm_clock_seqlock,
                          &timers_state.vm_clock_lock);
 }
 
 static void icount_adjust_rt(void *opaque)
 {
     timer_mod(timers_state.icount_rt_timer,
               qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL_RT) + 1000);
     icount_adjust();
 }
 
 static void icount_adjust_vm(void *opaque)
 {
     timer_mod(timers_state.icount_vm_timer,
                    qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
                    NANOSECONDS_PER_SECOND / 10);
     icount_adjust();
 }
 
 int64_t icount_round(int64_t count)
 {
     int shift = qatomic_read(&timers_state.icount_time_shift);
     return (count + (1 << shift) - 1) >> shift;
 }
 
 static void icount_warp_rt(void)
 {
     unsigned seq;
     int64_t warp_start;
 
     /*
      * The icount_warp_timer is rescheduled soon after vm_clock_warp_start
      * changes from -1 to another value, so the race here is okay.
      */
     do {
         seq = seqlock_read_begin(&timers_state.vm_clock_seqlock);
         warp_start = timers_state.vm_clock_warp_start;
     } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, seq));
 
     if (warp_start == -1) {
         return;
     }
 
     seqlock_write_lock(&timers_state.vm_clock_seqlock,
                        &timers_state.vm_clock_lock);
     if (runstate_is_running()) {
         int64_t clock = REPLAY_CLOCK_LOCKED(REPLAY_CLOCK_VIRTUAL_RT,
                                             cpu_get_clock_locked());
         int64_t warp_delta;
 
         warp_delta = clock - timers_state.vm_clock_warp_start;
         if (icount_enabled() == 2) {
             /*
              * In adaptive mode, do not let QEMU_CLOCK_VIRTUAL run too
              * far ahead of real time.
              */
             int64_t cur_icount = icount_get_locked();
             int64_t delta = clock - cur_icount;
             warp_delta = MIN(warp_delta, delta);
         }
         qatomic_set_i64(&timers_state.qemu_icount_bias,
                         timers_state.qemu_icount_bias + warp_delta);
     }
     timers_state.vm_clock_warp_start = -1;
     seqlock_write_unlock(&timers_state.vm_clock_seqlock,
                        &timers_state.vm_clock_lock);
 
     if (qemu_clock_expired(QEMU_CLOCK_VIRTUAL)) {
         qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
     }
 }
 
 static void icount_timer_cb(void *opaque)
 {
     /*
      * No need for a checkpoint because the timer already synchronizes
      * with CHECKPOINT_CLOCK_VIRTUAL_RT.
      */
     icount_warp_rt();
 }
 
 void icount_start_warp_timer(void)
 {
     int64_t clock;
     int64_t deadline;
 
     assert(icount_enabled());
 
     /*
      * Nothing to do if the VM is stopped: QEMU_CLOCK_VIRTUAL timers
      * do not fire, so computing the deadline does not make sense.
      */
     if (!runstate_is_running()) {
         return;
     }
 
     if (replay_mode != REPLAY_MODE_PLAY) {
         if (!all_cpu_threads_idle()) {
             return;
         }
 
         if (qtest_enabled()) {
             /* When testing, qtest commands advance icount.  */
             return;
         }
 
         replay_checkpoint(CHECKPOINT_CLOCK_WARP_START);
     } else {
         /* warp clock deterministically in record/replay mode */
         if (!replay_checkpoint(CHECKPOINT_CLOCK_WARP_START)) {
             /*
              * vCPU is sleeping and warp can't be started.
              * It is probably a race condition: notification sent
              * to vCPU was processed in advance and vCPU went to sleep.
              * Therefore we have to wake it up for doing someting.
              */
             if (replay_has_event()) {
                 qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
             }
             return;
         }
     }
 
     /* We want to use the earliest deadline from ALL vm_clocks */
     clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT);
     deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL,
                                           ~QEMU_TIMER_ATTR_EXTERNAL);
     if (deadline < 0) {
         static bool notified;
         if (!icount_sleep && !notified) {
             warn_report("icount sleep disabled and no active timers");
             notified = true;
         }
         return;
     }
 
     if (deadline > 0) {
         /*
          * Ensure QEMU_CLOCK_VIRTUAL proceeds even when the virtual CPU goes to
          * sleep.  Otherwise, the CPU might be waiting for a future timer
          * interrupt to wake it up, but the interrupt never comes because
          * the vCPU isn't running any insns and thus doesn't advance the
          * QEMU_CLOCK_VIRTUAL.
          */
         if (!icount_sleep) {
             /*
              * We never let VCPUs sleep in no sleep icount mode.
              * If there is a pending QEMU_CLOCK_VIRTUAL timer we just advance
              * to the next QEMU_CLOCK_VIRTUAL event and notify it.
              * It is useful when we want a deterministic execution time,
              * isolated from host latencies.
              */
             seqlock_write_lock(&timers_state.vm_clock_seqlock,
                                &timers_state.vm_clock_lock);
             qatomic_set_i64(&timers_state.qemu_icount_bias,
                             timers_state.qemu_icount_bias + deadline);
             seqlock_write_unlock(&timers_state.vm_clock_seqlock,
                                  &timers_state.vm_clock_lock);
             qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
         } else {
             /*
              * We do stop VCPUs and only advance QEMU_CLOCK_VIRTUAL after some
              * "real" time, (related to the time left until the next event) has
              * passed. The QEMU_CLOCK_VIRTUAL_RT clock will do this.
              * This avoids that the warps are visible externally; for example,
              * you will not be sending network packets continuously instead of
              * every 100ms.
              */
             seqlock_write_lock(&timers_state.vm_clock_seqlock,
                                &timers_state.vm_clock_lock);
             if (timers_state.vm_clock_warp_start == -1
                 || timers_state.vm_clock_warp_start > clock) {
                 timers_state.vm_clock_warp_start = clock;
             }
             seqlock_write_unlock(&timers_state.vm_clock_seqlock,
                                  &timers_state.vm_clock_lock);
             timer_mod_anticipate(timers_state.icount_warp_timer,
                                  clock + deadline);
         }
     } else if (deadline == 0) {
         qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
     }
 }
 
 void icount_account_warp_timer(void)
 {
     if (!icount_sleep) {
         return;
     }
 
     /*
      * Nothing to do if the VM is stopped: QEMU_CLOCK_VIRTUAL timers
      * do not fire, so computing the deadline does not make sense.
      */
     if (!runstate_is_running()) {
         return;
     }
 
     replay_async_events();
 
     /* warp clock deterministically in record/replay mode */
     if (!replay_checkpoint(CHECKPOINT_CLOCK_WARP_ACCOUNT)) {
         return;
     }
 
     timer_del(timers_state.icount_warp_timer);
     icount_warp_rt();
 }
 
 void icount_configure(QemuOpts *opts, Error **errp)
 {
     const char *option = qemu_opt_get(opts, "shift");
     bool sleep = qemu_opt_get_bool(opts, "sleep", true);
     bool align = qemu_opt_get_bool(opts, "align", false);
     long time_shift = -1;
 
     if (!option) {
         if (qemu_opt_get(opts, "align") != NULL) {
             error_setg(errp, "Please specify shift option when using align");
         }
         return;
     }
 
     if (align && !sleep) {
         error_setg(errp, "align=on and sleep=off are incompatible");
         return;
     }
 
     if (strcmp(option, "auto") != 0) {
         if (qemu_strtol(option, NULL, 0, &time_shift) < 0
             || time_shift < 0 || time_shift > MAX_ICOUNT_SHIFT) {
             error_setg(errp, "icount: Invalid shift value");
             return;
         }
     } else if (icount_align_option) {
         error_setg(errp, "shift=auto and align=on are incompatible");
         return;
     } else if (!icount_sleep) {
         error_setg(errp, "shift=auto and sleep=off are incompatible");
         return;
     }
 
     icount_sleep = sleep;
     if (icount_sleep) {
         timers_state.icount_warp_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL_RT,
                                          icount_timer_cb, NULL);
     }
 
     icount_align_option = align;
 
     if (time_shift >= 0) {
         timers_state.icount_time_shift = time_shift;
         icount_enable_precise();
         return;
     }
 
     icount_enable_adaptive();
 
     /*
      * 125MIPS seems a reasonable initial guess at the guest speed.
      * It will be corrected fairly quickly anyway.
      */
     timers_state.icount_time_shift = 3;
 
     /*
      * Have both realtime and virtual time triggers for speed adjustment.
      * The realtime trigger catches emulated time passing too slowly,
      * the virtual time trigger catches emulated time passing too fast.
      * Realtime triggers occur even when idle, so use them less frequently
      * than VM triggers.
      */
     timers_state.vm_clock_warp_start = -1;
     timers_state.icount_rt_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL_RT,
                                    icount_adjust_rt, NULL);
     timer_mod(timers_state.icount_rt_timer,
                    qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL_RT) + 1000);
     timers_state.icount_vm_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
                                         icount_adjust_vm, NULL);
     timer_mod(timers_state.icount_vm_timer,
                    qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
                    NANOSECONDS_PER_SECOND / 10);
 }
 
 void icount_notify_exit(void)
 {
     if (icount_enabled() && current_cpu) {
         qemu_cpu_kick(current_cpu);
         qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
     }
 }