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cpus: protect TimerState writes with a spinlock
In the next patch, we will need to write cpu_ticks_offset from any thread, even outside the BQL. Currently, it is protected by the BQL just because cpu_enable_ticks and cpu_disable_ticks happen to hold it, but the critical sections are well delimited and it's easy to remove the BQL dependency. Add a spinlock that matches vm_clock_seqlock, and hold it when writing to the TimerState. This also lets us fix cpu_update_icount when 64-bit atomics are not available. Fields of TiemrState are reordered to avoid padding. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini
parent
988fcafc73
commit
94377115b2
72
cpus.c
72
cpus.c
@ -129,21 +129,27 @@ typedef struct TimersState {
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int64_t cpu_ticks_prev;
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int64_t cpu_ticks_offset;
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/* cpu_clock_offset can be read out of BQL, so protect it with
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* this lock.
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/* Protect fields that can be respectively read outside the
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* BQL, and written from multiple threads.
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*/
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QemuSeqLock vm_clock_seqlock;
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int64_t cpu_clock_offset;
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int32_t cpu_ticks_enabled;
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QemuSpin vm_clock_lock;
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int16_t cpu_ticks_enabled;
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/* Conversion factor from emulated instructions to virtual clock ticks. */
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int icount_time_shift;
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int16_t icount_time_shift;
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/* Compensate for varying guest execution speed. */
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int64_t qemu_icount_bias;
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int64_t vm_clock_warp_start;
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int64_t cpu_clock_offset;
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/* Only written by TCG thread */
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int64_t qemu_icount;
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/* for adjusting icount */
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int64_t vm_clock_warp_start;
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QEMUTimer *icount_rt_timer;
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QEMUTimer *icount_vm_timer;
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QEMUTimer *icount_warp_timer;
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@ -244,11 +250,15 @@ void cpu_update_icount(CPUState *cpu)
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int64_t executed = cpu_get_icount_executed(cpu);
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cpu->icount_budget -= executed;
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#ifdef CONFIG_ATOMIC64
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#ifndef CONFIG_ATOMIC64
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seqlock_write_lock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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#endif
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atomic_set__nocheck(&timers_state.qemu_icount,
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timers_state.qemu_icount + executed);
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#else /* FIXME: we need 64bit atomics to do this safely */
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timers_state.qemu_icount += executed;
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#ifndef CONFIG_ATOMIC64
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seqlock_write_unlock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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#endif
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}
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@ -369,14 +379,15 @@ int64_t cpu_get_clock(void)
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*/
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void cpu_enable_ticks(void)
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{
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/* Here, the really thing protected by seqlock is cpu_clock_offset. */
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seqlock_write_begin(&timers_state.vm_clock_seqlock);
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seqlock_write_lock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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if (!timers_state.cpu_ticks_enabled) {
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timers_state.cpu_ticks_offset -= cpu_get_host_ticks();
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timers_state.cpu_clock_offset -= get_clock();
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timers_state.cpu_ticks_enabled = 1;
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}
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seqlock_write_end(&timers_state.vm_clock_seqlock);
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seqlock_write_unlock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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}
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/* disable cpu_get_ticks() : the clock is stopped. You must not call
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@ -385,14 +396,15 @@ void cpu_enable_ticks(void)
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*/
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void cpu_disable_ticks(void)
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{
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/* Here, the really thing protected by seqlock is cpu_clock_offset. */
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seqlock_write_begin(&timers_state.vm_clock_seqlock);
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seqlock_write_lock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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if (timers_state.cpu_ticks_enabled) {
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timers_state.cpu_ticks_offset += cpu_get_host_ticks();
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timers_state.cpu_clock_offset = cpu_get_clock_locked();
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timers_state.cpu_ticks_enabled = 0;
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}
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seqlock_write_end(&timers_state.vm_clock_seqlock);
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seqlock_write_unlock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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}
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/* Correlation between real and virtual time is always going to be
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@ -415,7 +427,8 @@ static void icount_adjust(void)
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return;
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}
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seqlock_write_begin(&timers_state.vm_clock_seqlock);
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seqlock_write_lock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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cur_time = cpu_get_clock_locked();
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cur_icount = cpu_get_icount_locked();
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@ -439,7 +452,8 @@ static void icount_adjust(void)
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atomic_set__nocheck(&timers_state.qemu_icount_bias,
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cur_icount - (timers_state.qemu_icount
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<< timers_state.icount_time_shift));
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seqlock_write_end(&timers_state.vm_clock_seqlock);
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seqlock_write_unlock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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}
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static void icount_adjust_rt(void *opaque)
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@ -480,7 +494,8 @@ static void icount_warp_rt(void)
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return;
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}
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seqlock_write_begin(&timers_state.vm_clock_seqlock);
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seqlock_write_lock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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if (runstate_is_running()) {
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int64_t clock = REPLAY_CLOCK(REPLAY_CLOCK_VIRTUAL_RT,
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cpu_get_clock_locked());
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@ -500,7 +515,8 @@ static void icount_warp_rt(void)
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timers_state.qemu_icount_bias + warp_delta);
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}
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timers_state.vm_clock_warp_start = -1;
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seqlock_write_end(&timers_state.vm_clock_seqlock);
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seqlock_write_unlock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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if (qemu_clock_expired(QEMU_CLOCK_VIRTUAL)) {
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qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
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@ -525,10 +541,12 @@ void qtest_clock_warp(int64_t dest)
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int64_t deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL);
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int64_t warp = qemu_soonest_timeout(dest - clock, deadline);
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seqlock_write_begin(&timers_state.vm_clock_seqlock);
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seqlock_write_lock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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atomic_set__nocheck(&timers_state.qemu_icount_bias,
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timers_state.qemu_icount_bias + warp);
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seqlock_write_end(&timers_state.vm_clock_seqlock);
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seqlock_write_unlock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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qemu_clock_run_timers(QEMU_CLOCK_VIRTUAL);
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timerlist_run_timers(aio_context->tlg.tl[QEMU_CLOCK_VIRTUAL]);
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@ -595,10 +613,12 @@ void qemu_start_warp_timer(void)
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* It is useful when we want a deterministic execution time,
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* isolated from host latencies.
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*/
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seqlock_write_begin(&timers_state.vm_clock_seqlock);
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seqlock_write_lock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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atomic_set__nocheck(&timers_state.qemu_icount_bias,
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timers_state.qemu_icount_bias + deadline);
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seqlock_write_end(&timers_state.vm_clock_seqlock);
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seqlock_write_unlock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
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} else {
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/*
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@ -609,12 +629,14 @@ void qemu_start_warp_timer(void)
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* you will not be sending network packets continuously instead of
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* every 100ms.
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*/
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seqlock_write_begin(&timers_state.vm_clock_seqlock);
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seqlock_write_lock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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if (timers_state.vm_clock_warp_start == -1
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|| timers_state.vm_clock_warp_start > clock) {
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timers_state.vm_clock_warp_start = clock;
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}
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seqlock_write_end(&timers_state.vm_clock_seqlock);
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seqlock_write_unlock(&timers_state.vm_clock_seqlock,
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&timers_state.vm_clock_lock);
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timer_mod_anticipate(timers_state.icount_warp_timer,
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clock + deadline);
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}
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