void qemu_clock_warp(QEMUClockType type) { int64_t deadline; /* * There are too many global variables to make the "warp" behavior * applicable to other clocks. But a clock argument removes the * need for if statements all over the place. */ if (type != QEMU_CLOCK_VIRTUAL || !use_icount) { return; } /* * If the CPUs have been sleeping, advance QEMU_CLOCK_VIRTUAL timer now. * This ensures that the deadline for the timer is computed correctly below. * This also makes sure that the insn counter is synchronized before the * CPU starts running, in case the CPU is woken by an event other than * the earliest QEMU_CLOCK_VIRTUAL timer. */ icount_warp_rt(NULL); if (!all_cpu_threads_idle() || !qemu_clock_has_timers(QEMU_CLOCK_VIRTUAL)) { timer_del(icount_warp_timer); return; } if (qtest_enabled()) { /* When testing, qtest commands advance icount. */ return; } vm_clock_warp_start = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); /* We want to use the earliest deadline from ALL vm_clocks */ deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL); /* Maintain prior (possibly buggy) behaviour where if no deadline * was set (as there is no QEMU_CLOCK_VIRTUAL timer) or it is more than * INT32_MAX nanoseconds ahead, we still use INT32_MAX * nanoseconds. */ if ((deadline < 0) || (deadline > INT32_MAX)) { deadline = INT32_MAX; } 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. * * An extreme solution for this problem would be to never let VCPUs * sleep in icount mode if there is a pending QEMU_CLOCK_VIRTUAL * timer; rather time could just advance to the next QEMU_CLOCK_VIRTUAL * event. Instead, we do stop VCPUs and only advance QEMU_CLOCK_VIRTUAL * after some e"real" time, (related to the time left until the next * event) has passed. The QEMU_CLOCK_REALTIME timer 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. */ timer_mod(icount_warp_timer, vm_clock_warp_start + deadline); } else if (deadline == 0) { qemu_clock_notify(QEMU_CLOCK_VIRTUAL); } }