Hi Wanpeng, > > On 11/05/2017 14:07, Zhoujian (jay) wrote: > >> - * Scan sptes if dirty logging has been stopped, dropping those > >> - * which can be collapsed into a single large-page spte. Later > >> - * page faults will create the large-page sptes. > >> + * Reset each vcpu's mmu, then page faults will create the > large-page > >> + * sptes later. > >> */ > >> if ((change != KVM_MR_DELETE) && > >> (old->flags & KVM_MEM_LOG_DIRTY_PAGES) && > >> - !(new->flags & KVM_MEM_LOG_DIRTY_PAGES)) > >> - kvm_mmu_zap_collapsible_sptes(kvm, new); > > This is an unlikely branch(unless guest live migration fails and continue > to run on the source machine) instead of hot path, do you have any > performance number for your real workloads? >
Sorry to bother you again. Recently, I have tested the performance before migration and after migration failure using spec cpu2006 https://www.spec.org/cpu2006/, which is a standard performance evaluation tool. These are the results: ****** Before migration the score is 153, and the TLB miss statistics of the qemu process is: linux-sjrfac:/mnt/zhoujian # perf stat -e dTLB-load-misses,dTLB-loads,dTLB-store-misses, \ dTLB-stores,iTLB-load-misses,iTLB-loads -p 26463 sleep 10 Performance counter stats for process id '26463': 698,938 dTLB-load-misses # 0.13% of all dTLB cache hits (50.46%) 543,303,875 dTLB-loads (50.43%) 199,597 dTLB-store-misses (16.51%) 60,128,561 dTLB-stores (16.67%) 69,986 iTLB-load-misses # 6.17% of all iTLB cache hits (16.67%) 1,134,097 iTLB-loads (33.33%) 10.000684064 seconds time elapsed After migration failure the score is 149, and the TLB miss statistics of the qemu process is: linux-sjrfac:/mnt/zhoujian # perf stat -e dTLB-load-misses,dTLB-loads,dTLB-store-misses, \ dTLB-stores,iTLB-load-misses,iTLB-loads -p 26463 sleep 10 Performance counter stats for process id '26463': 765,400 dTLB-load-misses # 0.14% of all dTLB cache hits (50.50%) 540,972,144 dTLB-loads (50.47%) 207,670 dTLB-store-misses (16.50%) 58,363,787 dTLB-stores (16.67%) 109,772 iTLB-load-misses # 9.52% of all iTLB cache hits (16.67%) 1,152,784 iTLB-loads (33.32%) 10.000703078 seconds time elapsed ****** These are the steps: ====== (1) the version of kmod is 4.4.11(with slightly modified) and the version of qemu is 2.6.0 (with slightly modified), the kmod is applied with the following patch according to Paolo's advice: diff --git a/source/x86/x86.c b/source/x86/x86.c index 054a7d3..75a4bb3 100644 --- a/source/x86/x86.c +++ b/source/x86/x86.c @@ -8550,8 +8550,10 @@ void kvm_arch_commit_memory_region(struct kvm *kvm, */ if ((change != KVM_MR_DELETE) && (old->flags & KVM_MEM_LOG_DIRTY_PAGES) && - !(new->flags & KVM_MEM_LOG_DIRTY_PAGES)) - kvm_mmu_zap_collapsible_sptes(kvm, new); + !(new->flags & KVM_MEM_LOG_DIRTY_PAGES)) { + printk(KERN_ERR "zj make KVM_REQ_MMU_RELOAD request\n"); + kvm_make_all_cpus_request(kvm, KVM_REQ_MMU_RELOAD); + } /* * Set up write protection and/or dirty logging for the new slot. (2) I started up a memory preoccupied 10G VM(suse11sp3), which means its "RES column" in top is 10G, in order to set up the EPT table in advance. (3) And then, I run the test case 429.mcf of spec cpu2006 before migration and after migration failure. The 429.mcf is a memory intensive workload, and the migration failure is constructed deliberately with the following patch of qemu: diff --git a/migration/migration.c b/migration/migration.c index 5d725d0..88dfc59 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -625,6 +625,9 @@ static void process_incoming_migration_co(void *opaque) MIGRATION_STATUS_ACTIVE); ret = qemu_loadvm_state(f); + // deliberately construct the migration failure + exit(EXIT_FAILURE); + ps = postcopy_state_get(); trace_process_incoming_migration_co_end(ret, ps); if (ps != POSTCOPY_INCOMING_NONE) { ====== Results of the score and TLB miss rate are almost the same, and I am confused. May I ask which tool do you use to evaluate the performance? And if my test steps are wrong, please let me know, thank you. Regards, Jay Zhou