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Mon, 26 Jun 2023 04:14:56 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ4TidpIRvn310vMeZRKWvmGJ0MhuEQ2ARFZe5rT1NoWGq1vw0tlcgyejNgi6ZpWHm1o+VVAhQ== X-Received: by 2002:a7b:c392:0:b0:3fa:8fb1:50fe with SMTP id s18-20020a7bc392000000b003fa8fb150femr2593382wmj.15.1687778095812; Mon, 26 Jun 2023 04:14:55 -0700 (PDT) Received: from [192.168.10.118] ([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id z3-20020a5d4d03000000b0030aec5e020fsm7032393wrt.86.2023.06.26.04.14.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Jun 2023 04:14:55 -0700 (PDT) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: Marcelo Tosatti Subject: [PULL 06/18] kvm: reuse per-vcpu stats fd to avoid vcpu interruption Date: Mon, 26 Jun 2023 13:14:33 +0200 Message-ID: <20230626111445.163573-7-pbonzini@redhat.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230626111445.163573-1-pbonzini@redhat.com> References: <20230626111445.163573-1-pbonzini@redhat.com> MIME-Version: 1.0 Received-SPF: pass client-ip=170.10.129.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org From: Marcelo Tosatti A regression has been detected in latency testing of KVM guests. More specifically, it was observed that the cyclictest numbers inside of an isolated vcpu (running on isolated pcpu) are: Where a maximum of 50us is acceptable. The implementation of KVM_GET_STATS_FD uses run_on_cpu to query per vcpu statistics, which interrupts the vcpu (and is unnecessary). To fix this, open the per vcpu stats fd on vcpu initialization, and read from that fd from QEMU's main thread. Signed-off-by: Marcelo Tosatti Signed-off-by: Paolo Bonzini --- accel/kvm/kvm-all.c | 30 +++++++++++++++--------------- include/hw/core/cpu.h | 1 + 2 files changed, 16 insertions(+), 15 deletions(-) diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index 7679f397aec..9aa898db142 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -450,6 +450,8 @@ int kvm_init_vcpu(CPUState *cpu, Error **errp) "kvm_init_vcpu: kvm_arch_init_vcpu failed (%lu)", kvm_arch_vcpu_id(cpu)); } + cpu->kvm_vcpu_stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL); + err: return ret; } @@ -4007,7 +4009,7 @@ static StatsDescriptors *find_stats_descriptors(StatsTarget target, int stats_fd /* Read stats header */ kvm_stats_header = &descriptors->kvm_stats_header; - ret = read(stats_fd, kvm_stats_header, sizeof(*kvm_stats_header)); + ret = pread(stats_fd, kvm_stats_header, sizeof(*kvm_stats_header), 0); if (ret != sizeof(*kvm_stats_header)) { error_setg(errp, "KVM stats: failed to read stats header: " "expected %zu actual %zu", @@ -4038,7 +4040,8 @@ static StatsDescriptors *find_stats_descriptors(StatsTarget target, int stats_fd } static void query_stats(StatsResultList **result, StatsTarget target, - strList *names, int stats_fd, Error **errp) + strList *names, int stats_fd, CPUState *cpu, + Error **errp) { struct kvm_stats_desc *kvm_stats_desc; struct kvm_stats_header *kvm_stats_header; @@ -4096,7 +4099,7 @@ static void query_stats(StatsResultList **result, StatsTarget target, break; case STATS_TARGET_VCPU: add_stats_entry(result, STATS_PROVIDER_KVM, - current_cpu->parent_obj.canonical_path, + cpu->parent_obj.canonical_path, stats_list); break; default: @@ -4133,10 +4136,9 @@ static void query_stats_schema(StatsSchemaList **result, StatsTarget target, add_stats_schema(result, STATS_PROVIDER_KVM, target, stats_list); } -static void query_stats_vcpu(CPUState *cpu, run_on_cpu_data data) +static void query_stats_vcpu(CPUState *cpu, StatsArgs *kvm_stats_args) { - StatsArgs *kvm_stats_args = (StatsArgs *) data.host_ptr; - int stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL); + int stats_fd = cpu->kvm_vcpu_stats_fd; Error *local_err = NULL; if (stats_fd == -1) { @@ -4145,14 +4147,13 @@ static void query_stats_vcpu(CPUState *cpu, run_on_cpu_data data) return; } query_stats(kvm_stats_args->result.stats, STATS_TARGET_VCPU, - kvm_stats_args->names, stats_fd, kvm_stats_args->errp); - close(stats_fd); + kvm_stats_args->names, stats_fd, cpu, + kvm_stats_args->errp); } -static void query_stats_schema_vcpu(CPUState *cpu, run_on_cpu_data data) +static void query_stats_schema_vcpu(CPUState *cpu, StatsArgs *kvm_stats_args) { - StatsArgs *kvm_stats_args = (StatsArgs *) data.host_ptr; - int stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL); + int stats_fd = cpu->kvm_vcpu_stats_fd; Error *local_err = NULL; if (stats_fd == -1) { @@ -4162,7 +4163,6 @@ static void query_stats_schema_vcpu(CPUState *cpu, run_on_cpu_data data) } query_stats_schema(kvm_stats_args->result.schema, STATS_TARGET_VCPU, stats_fd, kvm_stats_args->errp); - close(stats_fd); } static void query_stats_cb(StatsResultList **result, StatsTarget target, @@ -4180,7 +4180,7 @@ static void query_stats_cb(StatsResultList **result, StatsTarget target, error_setg_errno(errp, errno, "KVM stats: ioctl failed"); return; } - query_stats(result, target, names, stats_fd, errp); + query_stats(result, target, names, stats_fd, NULL, errp); close(stats_fd); break; } @@ -4194,7 +4194,7 @@ static void query_stats_cb(StatsResultList **result, StatsTarget target, if (!apply_str_list_filter(cpu->parent_obj.canonical_path, targets)) { continue; } - run_on_cpu(cpu, query_stats_vcpu, RUN_ON_CPU_HOST_PTR(&stats_args)); + query_stats_vcpu(cpu, &stats_args); } break; } @@ -4220,6 +4220,6 @@ void query_stats_schemas_cb(StatsSchemaList **result, Error **errp) if (first_cpu) { stats_args.result.schema = result; stats_args.errp = errp; - run_on_cpu(first_cpu, query_stats_schema_vcpu, RUN_ON_CPU_HOST_PTR(&stats_args)); + query_stats_schema_vcpu(first_cpu, &stats_args); } } diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h index 4871ad85f07..3b765beb9b1 100644 --- a/include/hw/core/cpu.h +++ b/include/hw/core/cpu.h @@ -402,6 +402,7 @@ struct CPUState { struct kvm_dirty_gfn *kvm_dirty_gfns; uint32_t kvm_fetch_index; uint64_t dirty_pages; + int kvm_vcpu_stats_fd; /* Use by accel-block: CPU is executing an ioctl() */ QemuLockCnt in_ioctl_lock;