riscv/qemu: QEMU main repository: Please see https://www.qemu.org/docs/master/devel/submitting-a-patch.html for how to submit changes to QEMU. Pull Requests are ignored. Please only use release tarballs from the QEMU website. http://www.qemu.org - qemu

QEMU main repository: Please see https://www.qemu.org/docs/master/devel/submitting-a-patch.html for how to submit changes to QEMU. Pull Requests are ignored. Please only use release tarballs from the QEMU website. http://www.qemu.org

emulation kvm qemu virtualization

History

Paolo Bonzini 6b8f0187a4 icount: process QEMU_CLOCK_VIRTUAL timers in vCPU thread icount has become much slower after tcg_cpu_exec has stopped using the BQL. There is also a latent bug that is masked by the slowness. The slowness happens because every occurrence of a QEMU_CLOCK_VIRTUAL timer now has to wake up the I/O thread and wait for it. The rendez-vous is mediated by the BQL QemuMutex: - handle_icount_deadline wakes up the I/O thread with BQL taken - the I/O thread wakes up and waits on the BQL - the VCPU thread releases the BQL a little later - the I/O thread raises an interrupt, which calls qemu_cpu_kick - the VCPU thread notices the interrupt, takes the BQL to process it and waits on it All this back and forth is extremely expensive, causing a 6 to 8-fold slowdown when icount is turned on. One may think that the issue is that the VCPU thread is too dependent on the BQL, but then the latent bug comes in. I first tried removing the BQL completely from the x86 cpu_exec, only to see everything break. The only way to fix it (and make everything slow again) was to add a dummy BQL lock/unlock pair. This is because in -icount mode you really have to process the events before the CPU restarts executing the next instruction. Therefore, this series moves the processing of QEMU_CLOCK_VIRTUAL timers straight in the vCPU thread when running in icount mode. The required changes include: - make the timer notification callback wake up TCG's single vCPU thread when run from another thread. By using async_run_on_cpu, the callback can override all_cpu_threads_idle() when the CPU is halted. - move handle_icount_deadline after qemu_tcg_wait_io_event, so that the timer notification callback is invoked after the dummy work item wakes up the vCPU thread - make handle_icount_deadline run the timers instead of just waking the I/O thread. - stop processing the timers in the main loop Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>		10 years ago
..
block	block: Fix error handling in bdrv_replace_in_backing_chain()	10 years ago
crypto	crypto: add CTR mode support	10 years ago
disas	Fix Thumb-1 BE32 execution and disassembly.	10 years ago
exec	memory_region: Fix name comments	10 years ago
fpu	softfloat: Add float128_to_uint32_round_to_zero()	10 years ago
hw	pseries: Don't expose PCIe extended config space on older machine types	10 years ago
io	io: make qio_channel_yield aware of AioContexts	10 years ago
libdecnumber	Clean up ill-advised or unusual header guards	10 years ago
migration	postcopy: Use temporary for placing zero huge pages	10 years ago
monitor	qmp: Dumb down how we run QMP command registration	10 years ago
net	eth: Extend vlan stripping functions	10 years ago
qapi	qapi: New qobject_input_visitor_new_str() for convenience	10 years ago
qemu	icount: process QEMU_CLOCK_VIRTUAL timers in vCPU thread	10 years ago
qom	Merge branch 'icount-update' into HEAD	10 years ago
standard-headers	update Linux headers to 4.11	10 years ago
sysemu	cpus: define QEMUTimerListNotifyCB for QEMU system emulation	10 years ago
ui	gtk-egl: add scanout_disable support	10 years ago
elf.h	nios2: Add usermode binaries emulation	10 years ago
glib-compat.h	glib-compat: add g_test_add_data_func_full fallback	10 years ago
qemu-common.h	Update copyright year	10 years ago
qemu-io.h	hmp: Request permissions in qemu-io	10 years ago
trace-tcg.h	trace: get rid of generated-events.h/generated-events.c	10 years ago