The goal here is to be able to scale temporally execution of qemu-user/system,
using a given number of instructions per second.
We define a virtual clock, that can be late or in advance compared to real time.
When we are in advance, we slow execution (by sleeping) until catching real
time.
Finally, we should be able to cleanup icount=auto mode completely, and keep
icount usage for determistic purposes only.
It is built upon new TCG Plugins inline ops (store + conditional callbacks), now
merged on master.
Example in user-mode:
- Retrieve number of instructions to execute /bin/true
$ ./build/qemu-x86_64 -plugin ./build/tests/plugin/libinsn.so -d plugin
/bin/true
cpu 0 insns: 120546
total insns: 120546
- Slow execution to match 5 seconds
$ time ./build/qemu-x86_64 -plugin
./build/contrib/plugins/libips,ips=$((120546/5)) /bin/true
real 0m4.985s
Tested in system mode by booting a full debian system, and using:
$ sysbench cpu run
Performance decrease linearly with the given number of ips.
v2
--
- Added missing personal Signed-off-by for commits from Alex
- Fix bad rebase in stubs/meson.build
- move qtest_{get,set}_virtual_clock to accel/qtest/qtest.c
- A race condition was identified for plugins init/idle/resume, but is not
related to this series, and will be fixed in another one:
https://lore.kernel.org/qemu-devel/20240529152219.825680-1-alex.ben...@linaro.org/
v3
--
- remove precise execution (per insn, per tb is enough)
- fixed algorithm used. Instead of comparing from start time of the system, we
just check on a given quantum of time that we didn't run too fast. It is more
simple, there is no need to track idle/resume events, and a vcpu can sleep
correctly.
- use "sysbench cpu run" in system mode to check execution is slowed as
expected.
- do not use idle/resume callback
Alex Bennée (4):
sysemu: add set_virtual_time to accel ops
qtest: use cpu interface in qtest_clock_warp
sysemu: generalise qtest_warp_clock as qemu_clock_advance_virtual_time
plugins: add time control API
Pierrick Bouvier (2):
qtest: move qtest_{get,set}_virtual_clock to accel/qtest/qtest.c
contrib/plugins: add ips plugin example for cost modeling
include/qemu/qemu-plugin.h | 23 +++
include/qemu/timer.h | 15 ++
include/sysemu/accel-ops.h | 18 +-
include/sysemu/cpu-timers.h | 3 +-
include/sysemu/qtest.h | 2 -
accel/qtest/qtest.c | 13 ++
contrib/plugins/ips.c | 164 ++++++++++++++++++
plugins/api.c | 31 ++++
...t-virtual-clock.c => cpus-virtual-clock.c} | 5 +
system/cpus.c | 11 ++
system/qtest.c | 37 +---
util/qemu-timer.c | 26 +++
contrib/plugins/Makefile | 1 +
plugins/qemu-plugins.symbols | 2 +
stubs/meson.build | 2 +-
15 files changed, 314 insertions(+), 39 deletions(-)
create mode 100644 contrib/plugins/ips.c
rename stubs/{cpus-get-virtual-clock.c => cpus-virtual-clock.c} (68%)
--
2.39.2
