| Demonstrations of kvm exit reasons, the Linux eBPF/bcc version. |
| |
| |
| Considering virtual machines' frequent exits can cause performance problems, |
| this tool aims to locate the frequent exited reasons and then find solutions |
| to reduce or even avoid the exit, by displaying the detail exit reasons and |
| the counts of each vm exit for all vms running on one physical machine. |
| |
| |
| Features of this tool |
| ===================== |
| |
| - Although there is a patch: [KVM: x86: add full vm-exit reason debug entries] |
| (https://patchwork.kernel.org/project/kvm/patch/[email protected]/) |
| trying to fill more vm-exit reason debug entries, just as the comments said, |
| the code allocates lots of memory that may never be consumed, misses some |
| arch-specific kvm causes, and can not do kernel aggregation. Instead bcc, as |
| a user space tool, can implement all these functions more easily and flexibly. |
| - The bcc python logic could provide nice kernel aggregation and custom output, |
| like collpasing all tids for one pid (e.i. one vm's qemu process id) with exit |
| reasons sorted in descending order. For more information, see the following |
| #USAGE message. |
| - The bpf in-kernel percpu_array and percpu_cache further improves performance. |
| For more information, see the following #Help to understand. |
| |
| |
| Limited |
| ======= |
| |
| In view of the hardware-assisted virtualization technology of |
| different architectures, currently we only adapt on vmx in intel. |
| And the amd feature is on the road.. |
| |
| |
| Example output: |
| =============== |
| |
| # ./kvmexit.py |
| Display kvm exit reasons and statistics for all threads... Hit Ctrl-C to end. |
| PID TID KVM_EXIT_REASON COUNT |
| ^C1273551 1273568 EXIT_REASON_HLT 12 |
| 1273551 1273568 EXIT_REASON_MSR_WRITE 6 |
| 1274253 1274261 EXIT_REASON_EXTERNAL_INTERRUPT 1 |
| 1274253 1274261 EXIT_REASON_HLT 12 |
| 1274253 1274261 EXIT_REASON_MSR_WRITE 4 |
| |
| # ./kvmexit.py 6 |
| Display kvm exit reasons and statistics for all threads after sleeping 6 secs. |
| PID TID KVM_EXIT_REASON COUNT |
| 1273903 1273922 EXIT_REASON_EXTERNAL_INTERRUPT 175 |
| 1273903 1273922 EXIT_REASON_CPUID 10 |
| 1273903 1273922 EXIT_REASON_HLT 6043 |
| 1273903 1273922 EXIT_REASON_IO_INSTRUCTION 24 |
| 1273903 1273922 EXIT_REASON_MSR_WRITE 15025 |
| 1273903 1273922 EXIT_REASON_PAUSE_INSTRUCTION 11 |
| 1273903 1273922 EXIT_REASON_EOI_INDUCED 12 |
| 1273903 1273922 EXIT_REASON_EPT_VIOLATION 6 |
| 1273903 1273922 EXIT_REASON_EPT_MISCONFIG 380 |
| 1273903 1273922 EXIT_REASON_PREEMPTION_TIMER 194 |
| 1273551 1273568 EXIT_REASON_EXTERNAL_INTERRUPT 18 |
| 1273551 1273568 EXIT_REASON_HLT 989 |
| 1273551 1273568 EXIT_REASON_IO_INSTRUCTION 10 |
| 1273551 1273568 EXIT_REASON_MSR_WRITE 2205 |
| 1273551 1273568 EXIT_REASON_PAUSE_INSTRUCTION 1 |
| 1273551 1273568 EXIT_REASON_EOI_INDUCED 5 |
| 1273551 1273568 EXIT_REASON_EPT_MISCONFIG 61 |
| 1273551 1273568 EXIT_REASON_PREEMPTION_TIMER 14 |
| |
| # ./kvmexit.py -p 1273795 5 |
| Display kvm exit reasons and statistics for PID 1273795 after sleeping 5 secs. |
| KVM_EXIT_REASON COUNT |
| MSR_WRITE 13467 |
| HLT 5060 |
| PREEMPTION_TIMER 345 |
| EPT_MISCONFIG 264 |
| EXTERNAL_INTERRUPT 169 |
| EPT_VIOLATION 18 |
| PAUSE_INSTRUCTION 6 |
| IO_INSTRUCTION 4 |
| EOI_INDUCED 2 |
| |
| # ./kvmexit.py -p 1273795 5 -a |
| Display kvm exit reasons and statistics for PID 1273795 and its all threads after sleeping 5 secs. |
| TID KVM_EXIT_REASON COUNT |
| 1273819 EXTERNAL_INTERRUPT 64 |
| 1273819 HLT 2802 |
| 1273819 IO_INSTRUCTION 4 |
| 1273819 MSR_WRITE 7196 |
| 1273819 PAUSE_INSTRUCTION 2 |
| 1273819 EOI_INDUCED 2 |
| 1273819 EPT_VIOLATION 6 |
| 1273819 EPT_MISCONFIG 162 |
| 1273819 PREEMPTION_TIMER 194 |
| 1273820 EXTERNAL_INTERRUPT 78 |
| 1273820 HLT 2054 |
| 1273820 MSR_WRITE 5199 |
| 1273820 EPT_VIOLATION 2 |
| 1273820 EPT_MISCONFIG 77 |
| 1273820 PREEMPTION_TIMER 102 |
| |
| # ./kvmexit.py -p 1273795 -v 0 |
| Display kvm exit reasons and statistics for PID 1273795 VCPU 0... Hit Ctrl-C to end. |
| KVM_EXIT_REASON COUNT |
| ^CMSR_WRITE 2076 |
| HLT 795 |
| PREEMPTION_TIMER 86 |
| EXTERNAL_INTERRUPT 20 |
| EPT_MISCONFIG 10 |
| PAUSE_INSTRUCTION 2 |
| IO_INSTRUCTION 2 |
| EPT_VIOLATION 1 |
| EOI_INDUCED 1 |
| |
| # ./kvmexit.py -p 1273795 -v 0 4 |
| Display kvm exit reasons and statistics for PID 1273795 VCPU 0 after sleeping 4 secs. |
| KVM_EXIT_REASON COUNT |
| MSR_WRITE 4726 |
| HLT 1827 |
| PREEMPTION_TIMER 78 |
| EPT_MISCONFIG 67 |
| EXTERNAL_INTERRUPT 28 |
| IO_INSTRUCTION 4 |
| EOI_INDUCED 2 |
| PAUSE_INSTRUCTION 2 |
| |
| # ./kvmexit.py -p 1273795 -v 4 4 |
| Traceback (most recent call last): |
| File "tools/kvmexit.py", line 306, in <module> |
| raise Exception("There's no v%s for PID %d." % (tgt_vcpu, args.pid)) |
| Exception: There's no vCPU 4 for PID 1273795. |
| |
| # ./kvmexit.py -t 1273819 10 |
| Display kvm exit reasons and statistics for TID 1273819 after sleeping 10 secs. |
| KVM_EXIT_REASON COUNT |
| MSR_WRITE 13318 |
| HLT 5274 |
| EPT_MISCONFIG 263 |
| PREEMPTION_TIMER 171 |
| EXTERNAL_INTERRUPT 109 |
| IO_INSTRUCTION 8 |
| PAUSE_INSTRUCTION 5 |
| EOI_INDUCED 4 |
| EPT_VIOLATION 2 |
| |
| # ./kvmexit.py -T '1273820,1273819' |
| Display kvm exit reasons and statistics for TIDS ['1273820', '1273819']... Hit Ctrl-C to end. |
| TIDS KVM_EXIT_REASON COUNT |
| ^C1273819 EXTERNAL_INTERRUPT 300 |
| 1273819 HLT 13718 |
| 1273819 IO_INSTRUCTION 26 |
| 1273819 MSR_WRITE 37457 |
| 1273819 PAUSE_INSTRUCTION 13 |
| 1273819 EOI_INDUCED 13 |
| 1273819 EPT_VIOLATION 53 |
| 1273819 EPT_MISCONFIG 654 |
| 1273819 PREEMPTION_TIMER 958 |
| 1273820 EXTERNAL_INTERRUPT 212 |
| 1273820 HLT 9002 |
| 1273820 MSR_WRITE 25495 |
| 1273820 PAUSE_INSTRUCTION 2 |
| 1273820 EPT_VIOLATION 64 |
| 1273820 EPT_MISCONFIG 396 |
| 1273820 PREEMPTION_TIMER 268 |
| |
| |
| Help to understand |
| ================== |
| |
| We use a PERCPU_ARRAY: pcpuArrayA and a percpu_hash: hashA to collaboratively |
| store each kvm exit reason and its count. The reason is there exists a rule when |
| one vcpu exits and re-enters, it tends to continue to run on the same physical |
| cpu (pcpu as follows) as the last cycle, which is also called 'cache hit'. Thus |
| we turn to use a PERCPU_ARRAY to record the 'cache hit' situation to speed |
| things up; and for other cases, then use a percpu_hash. |
| |
| BTW, we originally use a common hash to do this, with a u64(exit_reason) |
| key and a struct exit_info {tgid_pid, exit_reason} value. But due to |
| the big lock in bpf_hash, each updating is quite performance consuming. |
| |
| Now imagine here is a pid_tgidA (vcpu A) exits and is going to run on |
| pcpuArrayA, the BPF code flow is as follows: |
| |
| pid_tgidA keeps running on the same pcpu |
| // \\ |
| // \\ |
| // Y N \\ |
| // \\ |
| a. cache_hit b. cache_miss |
| (cacheA's pid_tgid matches pid_tgidA) || |
| | || |
| | || |
| "increase percpu exit_ct and return" || |
| [*Note*] || |
| pid_tgidA ever been exited on pcpuArrayA? |
| // \\ |
| // \\ |
| // \\ |
| // Y N \\ |
| // \\ |
| b.a load_last_hashA b.b initialize_hashA_with_zero |
| \ / |
| \ / |
| \ / |
| "increase percpu exit_ct" |
| || |
| || |
| is another pid_tgid been running on pcpuArrayA? |
| // \\ |
| // Y N \\ |
| // \\ |
| b.*.a save_theLastHit_hashB do_nothing |
| \\ // |
| \\ // |
| \\ // |
| b.* save_to_pcpuArrayA |
| |
| |
| [*Note*] we do not update the table in above "a.", in case the vcpu hit the same |
| pcpu again when exits next time, instead we only update until this pcpu is not |
| hitted by the same tgidpid(vcpu) again, which is in "b.*.a" and "b.*". |
| |
| |
| USAGE message: |
| ============== |
| |
| # ./kvmexit.py -h |
| usage: kvmexit.py [-h] [-p PID [-v VCPU | -a] ] [-t TID | -T 'TID1,TID2'] [duration] |
| |
| Display kvm_exit_reason and its statistics at a timed interval |
| |
| optional arguments: |
| -h, --help show this help message and exit |
| -p PID, --pid PID display process with this PID only, collpase all tids with exit reasons sorted in descending order |
| -v VCPU, --v VCPU display this VCPU only for this PID |
| -a, --alltids display all TIDS for this PID |
| -t TID, --tid TID display thread with this TID only with exit reasons sorted in descending order |
| -T 'TID1,TID2', --tids 'TID1,TID2' |
| display threads for a union like {395490, 395491} |
| duration duration of display, after sleeping several seconds |
| |
| examples: |
| ./kvmexit # Display kvm_exit_reason and its statistics in real-time until Ctrl-C |
| ./kvmexit 5 # Display in real-time after sleeping 5s |
| ./kvmexit -p 3195281 # Collpase all tids for pid 3195281 with exit reasons sorted in descending order |
| ./kvmexit -p 3195281 20 # Collpase all tids for pid 3195281 with exit reasons sorted in descending order, and display after sleeping 20s |
| ./kvmexit -p 3195281 -v 0 # Display only vcpu0 for pid 3195281, descending sort by default |
| ./kvmexit -p 3195281 -a # Display all tids for pid 3195281 |
| ./kvmexit -t 395490 # Display only for tid 395490 with exit reasons sorted in descending order |
| ./kvmexit -t 395490 20 # Display only for tid 395490 with exit reasons sorted in descending order after sleeping 20s |
| ./kvmexit -T '395490,395491' # Display for a union like {395490, 395491} |
