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c2aa5f8199
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Sebastian Tanase c2aa5f8199 cpu-exec: Add sleeping algorithm 
The goal is to sleep qemu whenever the guest clock
is in advance compared to the host clock (we use
the monotonic clocks). The amount of time to sleep
is calculated in the execution loop in cpu_exec.

At first, we tried to approximate at each for loop the real time elapsed
while searching for a TB (generating or retrieving from cache) and
executing it. We would then approximate the virtual time corresponding
to the number of virtual instructions executed. The difference between
these 2 values would allow us to know if the guest is in advance or delayed.
However, the function used for measuring the real time
(qemu_clock_get_ns(QEMU_CLOCK_REALTIME)) proved to be very expensive.
We had an added overhead of 13% of the total run time.

Therefore, we modified the algorithm and only take into account the
difference between the 2 clocks at the begining of the cpu_exec function.
During the for loop we try to reduce the advance of the guest only by
computing the virtual time elapsed and sleeping if necessary. The overhead
is thus reduced to 3%. Even though this method still has a noticeable
overhead, it no longer is a bottleneck in trying to achieve a better
guest frequency for which the guest clock is faster than the host one.

As for the the alignement of the 2 clocks, with the first algorithm
the guest clock was oscillating between -1 and 1ms compared to the host clock.
Using the second algorithm we notice that the guest is 5ms behind the host, which
is still acceptable for our use case.

The tests where conducted using fio and stress. The host machine in an i5 CPU at
3.10GHz running Debian Jessie (kernel 3.12). The guest machine is an arm versatile-pb
built with buildroot.

Currently, on our test machine, the lowest icount we can achieve that is suitable for
aligning the 2 clocks is 6. However, we observe that the IO tests (using fio) are
slower than the cpu tests (using stress).

Signed-off-by: Sebastian Tanase <sebastian.tanase@openwide.fr>
Tested-by: Camille Bégué <camille.begue@openwide.fr>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2014-08-06 17:53:07 +02:00
audio audio: Drop superfluous conditionals around g_free() 2014-06-13 12:34:54 +02:00
backends backends: Introduce chr-testdev 2014-08-06 17:53:05 +02:00
block raw-posix: Fail gracefully if no working alignment is found 2014-07-18 13:18:43 +01:00
bsd-user bsd-user: Fix syscall format, add strace support for more syscalls 2014-06-11 00:25:06 +01:00
default-configs pc: implement pc-dimm device abstraction 2014-06-19 16:41:47 +03:00
disas disas/libvixl: prepend the include path of libvixl header files 2014-07-08 12:45:57 +01:00
docs docs: document missing VSERPORT_CHANGE event 2014-07-24 10:00:33 -04:00
dtc@bc895d6d09
fpu fpu: softfloat: drop INLINE macro 2014-06-23 11:00:12 -04:00
fsdev virtfs-proxy-helper: fix call to accept 2014-04-28 08:55:32 +04:00
gdb-xml
hw usb: mtp: tag root property as experimental 2014-07-23 08:55:40 +02:00
include cpu-exec: Add sleeping algorithm 2014-08-06 17:53:07 +02:00
libcacard vscclient: Add required headers to fix build on FreeBSD 2014-06-24 20:01:24 +04:00
libdecnumber libdecnumber: Fix decNumberSetBCD 2014-06-16 13:24:29 +02:00
linux-headers linux-headers: update linux headers to kvm/next 2014-06-16 13:24:41 +02:00
linux-user linux-user: use TARGET_SA_ONSTACK in get_sigframe 2014-07-15 17:08:41 +03:00
net slirp: Give error message if hostfwd_add/remove for unrecognized vlan/stack 2014-07-18 17:45:36 +04:00
pc-bios pc-bios/s390-ccw: update binary 2014-07-08 15:08:03 +02:00
pixman@97336fad32
po po: Update German translation 2014-07-28 23:37:17 +02:00
qapi block: add backing-file option to block-stream 2014-07-01 10:47:01 +02:00
qga qga: Add missing 'static' attribute 2014-07-18 17:45:37 +04:00
qobject json-lexer: fix escaped backslash in single-quoted string 2014-06-23 11:01:24 -04:00
qom qom: object: Ignore refs/unrefs of NULL 2014-07-01 10:20:41 +02:00
roms pseries: Update SLOF firmware image to qemu-slof-20140630 2014-07-08 12:10:36 +02:00
scripts vmstate static checker: detect section renames 2014-07-16 14:29:34 +05:30
slirp Increase maximum number of session of the internal TFTP server. 2014-06-24 20:01:24 +04:00
stubs backends: Introduce chr-testdev 2014-08-06 17:53:05 +02:00
sysconfigs/target
target-alpha softmmu: introduce cpu_ldst.h 2014-06-05 16:10:33 +02:00
target-arm target-arm: Implement vCPU reset via KVM_ARM_VCPU_INIT for 32-bit CPUs 2014-07-08 13:05:11 +01:00
target-cris target-cris/translate.c: Remove _t_gen_mov_TN_env and _t_gen_mov_env_TN 2014-06-09 01:04:44 +02:00
target-i386 target-i386: Allow execute from user mode when SMEP is enabled. 2014-07-15 18:43:14 +02:00
target-lm32 vl: allow other threads to do qemu_system_vmstop_request 2014-06-23 16:36:13 +08:00
target-m68k softmmu: introduce cpu_ldst.h 2014-06-05 16:10:33 +02:00
target-microblaze target-microblaze: Delete unused sign_extend() function 2014-06-10 19:39:34 +04:00
target-mips target-mips/translate.c: Free TCG in OPC_DINSV 2014-07-28 23:37:15 +02:00
target-moxie softmmu: introduce cpu_ldst.h 2014-06-05 16:10:33 +02:00
target-openrisc openrisc: fix comment 2014-06-29 18:59:06 +03:00
target-ppc spapr: Move RMA memory region registration code 2014-07-15 16:11:59 +02:00
target-s390x s390x/kvm: synchronize guest floating point registers 2014-07-14 09:15:38 +02:00
target-sh4 softmmu: introduce cpu_ldst.h 2014-06-05 16:10:33 +02:00
target-sparc softmmu: introduce cpu_ldst.h 2014-06-05 16:10:33 +02:00
target-unicore32 target-unicore: Remove unused functions 2014-06-24 20:01:24 +04:00
target-xtensa softmmu: introduce cpu_ldst.h 2014-06-05 16:10:33 +02:00
tcg tcg/ppc: Fix support for 64-bit PPC MacOSX hosts 2014-06-29 11:38:50 +01:00
tests trivial patches for 2014-07-18 2014-07-18 16:59:29 +01:00
trace glib-compat.h: add new thread API emulation on top of pre-2.31 API 2014-06-10 07:44:01 +02:00
ui vnc update fix 2014-07-25 09:43:31 +02:00
util module: Don't complain when a module is absent 2014-07-18 14:57:35 +02:00
.exrc
.gitignore qapi: ignore generated event files 2014-06-27 09:27:55 -04:00
.gitmodules PPC: Add u-boot firmware for e500 2014-06-16 13:24:35 +02:00
.mailmap
.travis.yml trace: Multi-backend tracing 2014-06-09 15:43:40 +02:00
aio-posix.c AioContext: speed up aio_notify 2014-07-09 15:50:11 +02:00
aio-win32.c block: drop aio functions that operate on the main AioContext 2014-07-09 15:50:11 +02:00
arch_init.c migration: catch unknown flags in ram_load 2014-06-16 04:55:27 +02:00
async.c AioContext: speed up aio_notify 2014-07-09 15:50:11 +02:00
balloon.c qapi event: convert BALLOON_CHANGE 2014-06-23 11:12:28 -04:00
block-migration.c migration: Add missing 'static' attribute 2014-07-18 17:45:37 +04:00
block.c block: Add Error argument to bdrv_refresh_limits() 2014-07-18 13:18:43 +01:00
blockdev-nbd.c nbd: Shutdown socket before closing. 2014-06-30 12:50:12 +02:00
blockdev.c block: add backing-file option to block-stream 2014-07-01 10:47:01 +02:00
blockjob.c block: prefer aio_poll to qemu_aio_wait 2014-07-09 15:50:11 +02:00
bt-host.c
bt-vhci.c
Changelog
CODING_STYLE CODING_STYLE: Section about mixed declarations 2014-03-27 19:22:49 +04:00
configure Enforce stack protector usage 2014-07-10 17:06:29 +02:00
COPYING
COPYING.LIB
coroutine-gthread.c glib-compat.h: add new thread API emulation on top of pre-2.31 API 2014-06-10 07:44:01 +02:00
coroutine-sigaltstack.c
coroutine-ucontext.c
coroutine-win32.c coroutine-win32.c: Add noinline attribute to work around gcc bug 2014-06-26 14:08:14 +01:00
cpu-exec.c cpu-exec: Add sleeping algorithm 2014-08-06 17:53:07 +02:00
cpus.c cpu-exec: Add sleeping algorithm 2014-08-06 17:53:07 +02:00
cputlb.c softmmu: introduce cpu_ldst.h 2014-06-05 16:10:33 +02:00
device_tree.c
device-hotplug.c blockdev: Remove unused DriveInfo reference count 2014-06-16 17:23:19 +08:00
disas.c monitor: QEMU Monitor Instruction Disassembly Incorrect for PowerPC LE Mode 2014-06-16 13:24:26 +02:00
dma-helpers.c dma-helpers: Fix too long qiov 2014-07-14 12:03:21 +02:00
dump.c dump: Make DumpState and endian conversion routines available for arch-specific dump code 2014-06-16 13:24:36 +02:00
exec.c exec: fix migration with devices that use address_space_rw 2014-07-22 10:38:50 +02:00
gdbstub.c exec: Change cpu_breakpoint_{insert,remove{,_by_ref,_all}} argument 2014-03-13 19:20:48 +01:00
HACKING
hmp-commands.hx Add the vhost-user netdev backend to the command line 2014-06-19 18:44:18 +03:00
hmp.c block: add backing-file option to block-stream 2014-07-01 10:47:01 +02:00
hmp.h hmp: add info memdev 2014-06-19 18:44:21 +03:00
iohandler.c iohandler.c: Properly initialize sigaction struct 2014-05-24 00:07:29 +04:00
ioport.c
iothread.c AioContext: do not rely on aio_poll(ctx, true) result to end a loop 2014-07-14 12:03:20 +02:00
kvm-all.c kvm-all: Use 'tmpcpu' instead of 'cpu' in sub-looping to avoid 'cpu' be NULL 2014-07-22 12:38:17 +02:00
kvm-stub.c Add kvm_eventfds_enabled function 2014-06-19 16:41:54 +03:00
LICENSE
main-loop.c block: drop aio functions that operate on the main AioContext 2014-07-09 15:50:11 +02:00
MAINTAINERS MAINTAINERS: add Stefan Hajnoczi to IDE maintainers 2014-07-07 09:15:29 +02:00
Makefile PPC: e500: Actually install u-boot.e500 2014-07-08 12:10:37 +02:00
Makefile.objs qapi script: add event support 2014-06-23 11:01:25 -04:00
Makefile.target configure: Fix -lm test, so that tools can be compiled on hosts that require -lm 2014-07-01 10:36:28 +02:00
memory_mapping.c
memory.c memory: MemoryRegion: Add size property 2014-07-01 10:20:41 +02:00
migration-exec.c
migration-fd.c
migration-rdma.c rdma: bug fixes 2014-06-23 19:09:50 +02:00
migration-tcp.c Coverity: Fix failure path for qemu_accept in migration 2014-05-05 22:15:03 +02:00
migration-unix.c Coverity: Fix failure path for qemu_accept in migration 2014-05-05 22:15:03 +02:00
migration.c migration: catch unknown flags in ram_load 2014-06-16 04:55:27 +02:00
module-common.c module: implement module loading 2014-02-20 13:14:18 +01:00
monitor.c serial: poll the serial console with G_IO_HUP 2014-06-30 15:04:34 +02:00
nbd.c nbd: Handle NBD_OPT_LIST option. 2014-06-30 12:50:17 +02:00
numa.c numa: check for busy memory backend 2014-07-06 09:13:53 +03:00
os-posix.c oslib-posix: Fix build on FreeBSD 2014-03-13 14:34:16 +00:00
os-win32.c util: Split out exec_dir from os_find_datadir 2014-02-20 13:12:54 +01:00
page_cache.c migration: Plug memory leak in migrate-set-cache-size command 2014-06-10 19:54:43 +04:00
qapi-schema.json backends: Introduce chr-testdev 2014-08-06 17:53:05 +02:00
qdev-monitor.c qdev: Implement named GPIOs 2014-05-28 17:36:21 +02:00
qdict-test-data.txt
qemu-bridge-helper.c qemu-bridge-helper: Fix fd leak in main() 2014-06-27 10:39:10 +02:00
qemu-char.c backends: Introduce chr-testdev 2014-08-06 17:53:05 +02:00
qemu-coroutine-io.c
qemu-coroutine-lock.c
qemu-coroutine-sleep.c
qemu-coroutine.c
qemu-doc.texi doc: slirp supports ICMP echo if enabled in Linux 2014-07-18 17:45:37 +04:00
qemu-file.c Make qemu_peek_buffer loop until it gets it's data 2014-05-05 22:15:03 +02:00
qemu-img-cmds.hx
qemu-img.c qemu-img: Remove redundancy "ret = -1" 2014-07-18 17:45:37 +04:00
qemu-img.texi Fix nocow typos in manpage 2014-07-07 09:15:29 +02:00
qemu-io-cmds.c block: prefer aio_poll to qemu_aio_wait 2014-07-09 15:50:11 +02:00
qemu-io.c trace: Multi-backend tracing 2014-06-09 15:43:40 +02:00
qemu-log.c
qemu-nbd.c nbd: Shutdown socket before closing. 2014-06-30 12:50:12 +02:00
qemu-nbd.texi nbd: Miscellaneous typo fixes. 2014-05-24 00:07:29 +04:00
qemu-options-wrapper.h
qemu-options.h
qemu-options.hx icount: Add align option to icount 2014-08-06 17:53:07 +02:00
qemu-seccomp.c seccomp: add shmctl(), mlock(), and munlock() to the syscall whitelist 2014-04-25 14:52:03 -03:00
qemu-tech.texi
qemu-timer.c vl.c: remove init_clocks call from main 2014-05-09 20:57:32 +02:00
qemu.nsi
qemu.sasl sasl: Avoid 'Could not find keytab file' in syslog 2014-03-15 13:54:18 +04:00
qmp-commands.hx block: add backing-file option to block-stream 2014-07-01 10:47:01 +02:00
qmp.c qmp: show QOM properties in device-list-properties 2014-07-07 11:10:05 +02:00
qtest.c icount: Add QemuOpts for icount 2014-08-06 17:53:07 +02:00
README
rules.mak build-sys: introduce install-prog macro to install&strip binaries and use it 2014-06-24 20:01:24 +04:00
savevm.c savevm: check vmsd for migratability status 2014-06-25 23:54:57 +02:00
softmmu_template.h softmmu: move softmmu_template.h out of include/ 2014-06-05 16:10:33 +02:00
spice-qemu-char.c qemu-char: introduce qemu_chr_alloc 2014-06-23 11:12:28 -04:00
tcg-runtime.c tcg: Push tcg-runtime routines into exec/helper-* 2014-05-28 09:33:54 -07:00
tci.c Merge remote-tracking branch 'remotes/bonzini/softmmu-smap' into staging 2014-06-05 21:06:14 +01:00
thread-pool.c aio: Fix use-after-free in cancellation path 2014-05-28 14:28:46 +02:00
thunk.c
tpm.c Use error_is_set() only when necessary 2014-02-17 11:57:23 -05:00
trace-events trace: add qemu_system_powerdown_request and qemu_system_shutdown_request trace events 2014-07-01 10:56:13 +02:00
translate-all.c Fix new typos (found by codespell) 2014-06-24 20:01:24 +04:00
translate-all.h translate-all: Change tb_check_watchpoint() argument to CPUState 2014-03-13 19:20:48 +01:00
user-exec.c softmmu: introduce cpu_ldst.h 2014-06-05 16:10:33 +02:00
VERSION Update version for v2.1.0-rc3 release 2014-07-22 18:17:03 +01:00
version.rc
vl.c icount: Add align option to icount 2014-08-06 17:53:07 +02:00
vmstate.c vmstate: Add preallocation for migrating arrays (VMS_ALLOC flag) 2014-06-27 13:48:27 +02:00
xbzrle.c xbzrle.c: Avoid undefined behaviour with signed arithmetic 2014-04-18 10:33:36 +04:00
xen-common-stub.c xen: factor out common functions 2014-05-07 16:16:43 +00:00
xen-common.c xen: factor out common functions 2014-05-07 16:16:43 +00:00
xen-hvm-stub.c xen-hvm: Fix xen_hvm_init() to adjust pc memory layout 2014-06-23 17:50:04 +03:00
xen-hvm.c Fix new typos in comments (found by codespell) 2014-07-18 17:45:36 +04:00
xen-mapcache.c xen: build on ARM 2014-07-07 10:37:40 +00:00

README 

Read the documentation in qemu-doc.html or on http://wiki.qemu-project.org

- QEMU team