标签：kvm -- Tracing KVM disable EXIT QEMU define
# Tracing QEMU-KVM Interactions
But default in linux you can figure out how many times and for what reasons there is a VM Exit from a VM into the kvm kernel module.
However given the ubiquity of vhost and the ability of kvm to emulate most device models directly in the kernel, most of those VM exits do not result in a transition from host kernel into the QEMU. The transitions from VM -> kvm -> QEMU are typically the most expensive.
Here we try to figure out how many of the VM Exits result in the invocation of QEMU.
## Tracking VM-KVM Interactions
This can be done very simply with perf
```
sudo ./perf stat -e 'kvm:*' -a sleep 1s
```
This will give you statistics collected over 1s for all VM exits (across VMs)
You can also do this directly and get the full trace logs via
```
echo 1 > /sys/kernel/debug/tracing/events/kvm/enable
cat /sys/kernel/debug/tracing/trace_pipe
```
## Background
All *primary* exits from kvm to QEMU are via the return path of KVM_RUN ioctl. Fortunately for us QEMU already has built in instrumentation for tracing. We will leverage that to selectively trace the return path of KVM_RUN and record the exit reasons
There is a second class of KVM-QEMU interaction that go through the ioeventfs,irqfd mechanism which we will instrument later.
### Code that triggers tracing of the (explicit) kvm to qemu exit
https://github.com/qemu/qemu/blob/7e56accdaf35234b69c33c85e4a44a5d56325e53/accel/kvm/kvm-all.c#L2041
### QEMU Tracing Documentation
http://git.qemu.org/?p=qemu.git;a=blob_plain;f=docs/devel/tracing.txt;hb=HEAD
https://fossies.org/linux/qemu/docs/tracing.txt
# ftrace backend
Enabling this backend allows you to trace both the VM-KVM events as well the KVM-QEMU events.
### Build QEMU with tracking with ftrace backend
```
./configure --disable-bluez --disable-brlapi --disable-bzip2 --disable-curl --disable-curses --disable-debug-tcg --disable-fdt --disable-glusterfs --disable-gtk --disable-libiscsi --disable-libnfs --disable-libssh2 --disable-libusb --disable-linux-aio --disable-lzo --disable-opengl --disable-qom-cast-debug --disable-rbd --disable-rdma --disable-sdl --disable-seccomp --disable-slirp --disable-snappy --disable-spice --disable-strip --disable-tcg-interpreter --disable-tcmalloc --disable-tools --disable-tpm --disable-usb-redir --disable-uuid --disable-vnc --disable-vnc-jpeg --disable-vnc-png --disable-vnc-sasl --disable-vte --disable-xen --enable-attr --enable-cap-ng --enable-kvm --enable-virtfs --target-list=x86_64-softmmu --extra-cflags="-fno-semantic-interposition -O3 -falign-functions=32" --datadir=/usr/share/qemu-lite --libdir=/usr/lib64/qemu-lite --libexecdir=/usr/libexec/qemu-lite --enable-vhost-net --disable-docs --enable-trace-backends=ftrace
```
### Launch QEMU with tracing enabled
Enable the tracking of just the kvm_run exit.
```
rm -f /tmp/event
echo kvm_run_exit > /tmp/events
sudo ../x86_64-softmmu/qemu-system-x86_64 -trace events=/tmp/events -machine pc-lite,accel=kvm,kernel_irqchip,nvdimm -cpu host -m 256,maxmem=1G,slots=2 -smp 2 -no-user-config -nodefaults -rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=discard -kernel ./vmlinux-4.9.34-63.1.container -append "reboot=k panic=1 rw tsc=reliable no_timer_check noreplace-smp root=/dev/pmem0p1 init=/usr/lib/systemd/systemd initcall_debug rootfstype=ext4 rootflags=dax,data=ordered dhcp rcupdate.rcu_expedited=1 clocksource=kvm-clock console=hvc0 single iommu=false " -device virtio-serial-pci,id=virtio-serial0 -chardev pty,id=charconsole0 -device virtconsole,chardev=charconsole0,id=console0 -nographic -object memory-backend-file,id=mem0,share,mem-path=./clear-16160-containers.img,size=235929600 -device nvdimm,memdev=mem0,id=nv0 -no-reboot -device virtio-net-pci,netdev=net0,mac=DE:AD:BE:EF:07:83 -netdev tap,id=net0,ifname=net0,script=no,downscript=no,queues=2,vhost=off -qmp tcp:localhost:4444,server,nowait
```
### Tracing I/O interactions
The kvm_run exit only records the explicit control exits. However for handing I/O QEMU-KVM irqfd and ioeventfd interaction mechanism.
Unfortunately there does not exit a direct way to tap into the ioeventfd. However we can trace the actuall callback functions ultimately invoked.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d34e6b175e61821026893ec5298cc8e7558df43a
http://blog.allenx.org/2015/07/05/kvm-irqfd-and-ioeventfd
## Obtained the combined trace logs
If you had enabled kvm tracing before, you will see a mix of KVM exits as well as KVM to QEMU transistion traces.
```
cat /sys/kernel/debug/tracing/trace_pipe
```
## Simple Backend
The following example shows how to trace using the simple backend. This is another method that is simpler and directly creates trace files on disk.
### Build QEMU with tracing
```
./configure --disable-bluez --disable-brlapi --disable-bzip2 --disable-curl --disable-curses --disable-debug-tcg --disable-fdt --disable-glusterfs --disable-gtk --disable-libiscsi --disable-libnfs --disable-libssh2 --disable-libusb --disable-linux-aio --disable-lzo --disable-opengl --disable-qom-cast-debug --disable-rbd --disable-rdma --disable-sdl --disable-seccomp --disable-slirp --disable-snappy --disable-spice --disable-strip --disable-tcg-interpreter --disable-tcmalloc --disable-tools --disable-tpm --disable-usb-redir --disable-uuid --disable-vnc --disable-vnc-jpeg --disable-vnc-png --disable-vnc-sasl --disable-vte --disable-xen --enable-attr --enable-cap-ng --enable-kvm --enable-virtfs --target-list=x86_64-softmmu --extra-cflags="-fno-semantic-interposition -O3 -falign-functions=32" --datadir=/usr/share/qemu-lite --libdir=/usr/lib64/qemu-lite --libexecdir=/usr/libexec/qemu-lite --enable-vhost-net --disable-docs --enable-trace-backends=simple
```
### Launch QEMU with tracing enabled
```
rm -f /tmp/event
echo kvm_run_exit > /tmp/events
sudo ../x86_64-softmmu/qemu-system-x86_64 -trace events=/tmp/events -machine pc-lite,accel=kvm,kernel_irqchip,nvdimm -cpu host -m 256,maxmem=1G,slots=2 -smp 2 -no-user-config -nodefaults -rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=discard -kernel ./vmlinux-4.9.34-63.1.container -append "reboot=k panic=1 rw tsc=reliable no_timer_check noreplace-smp root=/dev/pmem0p1 init=/usr/lib/systemd/systemd initcall_debug rootfstype=ext4 rootflags=dax,data=ordered dhcp rcupdate.rcu_expedited=1 clocksource=kvm-clock console=hvc0 single iommu=false " -device virtio-serial-pci,id=virtio-serial0 -chardev pty,id=charconsole0 -device virtconsole,chardev=charconsole0,id=console0 -nographic -object memory-backend-file,id=mem0,share,mem-path=./clear-16160-containers.img,size=235929600 -device nvdimm,memdev=mem0,id=nv0 -no-reboot -device virtio-net-pci,netdev=net0,mac=DE:AD:BE:EF:07:83 -netdev tap,id=net0,ifname=net0,script=no,downscript=no,queues=2,vhost=off -qmp tcp:localhost:4444,server,nowait
```
### Analyze the Trace Events
```
simpletrace.py trace-events-all trace-6440 &> /tmp/xxx
```
Note:
- The trace-events-all file will be generated at the time of qemu compilation
- The trace-xyz file will be generated at qemu execution
## KVM-QEMU Exit Reasons
This will help you co-relate exit reasons to the trace logs.
Teh most common ones will be for IO (2), as these are used for device modeling.
https://github.com/qemu/qemu/blob/0748b3526e8cb78b9cd64208426bfc3d54a72b04/linux-headers/linux/kvm.h#L182
```
#define KVM_EXIT_UNKNOWN 0
#define KVM_EXIT_EXCEPTION 1
#define KVM_EXIT_IO 2
#define KVM_EXIT_HYPERCALL 3
#define KVM_EXIT_DEBUG 4
#define KVM_EXIT_HLT 5
#define KVM_EXIT_MMIO 6
#define KVM_EXIT_IRQ_WINDOW_OPEN 7
#define KVM_EXIT_SHUTDOWN 8
#define KVM_EXIT_FAIL_ENTRY 9
#define KVM_EXIT_INTR 10
#define KVM_EXIT_SET_TPR 11
#define KVM_EXIT_TPR_ACCESS 12
#define KVM_EXIT_S390_SIEIC 13
#define KVM_EXIT_S390_RESET 14
#define KVM_EXIT_DCR 15 /* deprecated */
#define KVM_EXIT_NMI 16
#define KVM_EXIT_INTERNAL_ERROR 17
#define KVM_EXIT_OSI 18
#define KVM_EXIT_PAPR_HCALL 19
#define KVM_EXIT_S390_UCONTROL 20
#define KVM_EXIT_WATCHDOG 21
#define KVM_EXIT_S390_TSCH 22
#define KVM_EXIT_EPR 23
#define KVM_EXIT_SYSTEM_EVENT 24
#define KVM_EXIT_S390_STSI 25
#define KVM_EXIT_IOAPIC_EOI 26
#define KVM_EXIT_HYPERV 27
```
# Tracing all events
All events supported by QEMU can be found in the trace-events-all file.
You can extract them all (or a subset) and feed them via a script such as the one below
```
cat trace-events-all | grep "(" | grep -v "#" | cut -f 1 -d "(" > /tmp/events
```
标签：kvm,--,Tracing,KVM,disable,EXIT,QEMU,define 来源： https://www.cnblogs.com/dream397/p/14156896.html
本站声明： 1. iCode9 技术分享网（下文简称本站）提供的所有内容，仅供技术学习、探讨和分享； 2. 关于本站的所有留言、评论、转载及引用，纯属内容发起人的个人观点，与本站观点和立场无关； 3. 关于本站的所有言论和文字，纯属内容发起人的个人观点，与本站观点和立场无关； 4. 本站文章均是网友提供，不完全保证技术分享内容的完整性、准确性、时效性、风险性和版权归属；如您发现该文章侵犯了您的权益，可联系我们第一时间进行删除； 5. 本站为非盈利性的个人网站，所有内容不会用来进行牟利，也不会利用任何形式的广告来间接获益，纯粹是为了广大技术爱好者提供技术内容和技术思想的分享性交流网站。