144 lines
5.8 KiB
Diff
144 lines
5.8 KiB
Diff
From 3b6f485275ae95a81eec589d2773b86ca9ddec4d Mon Sep 17 00:00:00 2001
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From: Marcelo Tosatti <mtosatti@redhat.com>
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Date: Sun, 18 Jun 2023 23:24:40 +0200
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Subject: [PATCH] kvm: reuse per-vcpu stats fd to avoid vcpu interruption
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A regression has been detected in latency testing of KVM guests.
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More specifically, it was observed that the cyclictest
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numbers inside of an isolated vcpu (running on isolated pcpu) are:
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Where a maximum of 50us is acceptable.
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The implementation of KVM_GET_STATS_FD uses run_on_cpu to query
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per vcpu statistics, which interrupts the vcpu (and is unnecessary).
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To fix this, open the per vcpu stats fd on vcpu initialization,
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and read from that fd from QEMU's main thread.
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Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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---
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accel/kvm/kvm-all.c | 30 +++++++++++++++---------------
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include/hw/core/cpu.h | 1 +
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2 files changed, 16 insertions(+), 15 deletions(-)
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diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
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index 7679f397aec0..9aa898db142e 100644
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--- a/accel/kvm/kvm-all.c
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+++ b/accel/kvm/kvm-all.c
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@@ -450,6 +450,8 @@ int kvm_init_vcpu(CPUState *cpu, Error **errp)
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"kvm_init_vcpu: kvm_arch_init_vcpu failed (%lu)",
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kvm_arch_vcpu_id(cpu));
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}
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+ cpu->kvm_vcpu_stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL);
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+
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err:
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return ret;
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}
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@@ -4007,7 +4009,7 @@ static StatsDescriptors *find_stats_descriptors(StatsTarget target, int stats_fd
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/* Read stats header */
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kvm_stats_header = &descriptors->kvm_stats_header;
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- ret = read(stats_fd, kvm_stats_header, sizeof(*kvm_stats_header));
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+ ret = pread(stats_fd, kvm_stats_header, sizeof(*kvm_stats_header), 0);
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if (ret != sizeof(*kvm_stats_header)) {
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error_setg(errp, "KVM stats: failed to read stats header: "
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"expected %zu actual %zu",
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@@ -4038,7 +4040,8 @@ static StatsDescriptors *find_stats_descriptors(StatsTarget target, int stats_fd
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}
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static void query_stats(StatsResultList **result, StatsTarget target,
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- strList *names, int stats_fd, Error **errp)
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+ strList *names, int stats_fd, CPUState *cpu,
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+ Error **errp)
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{
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struct kvm_stats_desc *kvm_stats_desc;
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struct kvm_stats_header *kvm_stats_header;
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@@ -4096,7 +4099,7 @@ static void query_stats(StatsResultList **result, StatsTarget target,
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break;
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case STATS_TARGET_VCPU:
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add_stats_entry(result, STATS_PROVIDER_KVM,
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- current_cpu->parent_obj.canonical_path,
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+ cpu->parent_obj.canonical_path,
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stats_list);
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break;
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default:
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@@ -4133,10 +4136,9 @@ static void query_stats_schema(StatsSchemaList **result, StatsTarget target,
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add_stats_schema(result, STATS_PROVIDER_KVM, target, stats_list);
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}
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-static void query_stats_vcpu(CPUState *cpu, run_on_cpu_data data)
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+static void query_stats_vcpu(CPUState *cpu, StatsArgs *kvm_stats_args)
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{
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- StatsArgs *kvm_stats_args = (StatsArgs *) data.host_ptr;
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- int stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL);
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+ int stats_fd = cpu->kvm_vcpu_stats_fd;
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Error *local_err = NULL;
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if (stats_fd == -1) {
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@@ -4145,14 +4147,13 @@ static void query_stats_vcpu(CPUState *cpu, run_on_cpu_data data)
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return;
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}
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query_stats(kvm_stats_args->result.stats, STATS_TARGET_VCPU,
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- kvm_stats_args->names, stats_fd, kvm_stats_args->errp);
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- close(stats_fd);
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+ kvm_stats_args->names, stats_fd, cpu,
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+ kvm_stats_args->errp);
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}
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-static void query_stats_schema_vcpu(CPUState *cpu, run_on_cpu_data data)
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+static void query_stats_schema_vcpu(CPUState *cpu, StatsArgs *kvm_stats_args)
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{
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- StatsArgs *kvm_stats_args = (StatsArgs *) data.host_ptr;
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- int stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL);
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+ int stats_fd = cpu->kvm_vcpu_stats_fd;
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Error *local_err = NULL;
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if (stats_fd == -1) {
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@@ -4162,7 +4163,6 @@ static void query_stats_schema_vcpu(CPUState *cpu, run_on_cpu_data data)
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}
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query_stats_schema(kvm_stats_args->result.schema, STATS_TARGET_VCPU, stats_fd,
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kvm_stats_args->errp);
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- close(stats_fd);
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}
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static void query_stats_cb(StatsResultList **result, StatsTarget target,
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@@ -4180,7 +4180,7 @@ static void query_stats_cb(StatsResultList **result, StatsTarget target,
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error_setg_errno(errp, errno, "KVM stats: ioctl failed");
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return;
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}
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- query_stats(result, target, names, stats_fd, errp);
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+ query_stats(result, target, names, stats_fd, NULL, errp);
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close(stats_fd);
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break;
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}
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@@ -4194,7 +4194,7 @@ static void query_stats_cb(StatsResultList **result, StatsTarget target,
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if (!apply_str_list_filter(cpu->parent_obj.canonical_path, targets)) {
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continue;
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}
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- run_on_cpu(cpu, query_stats_vcpu, RUN_ON_CPU_HOST_PTR(&stats_args));
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+ query_stats_vcpu(cpu, &stats_args);
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}
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break;
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}
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@@ -4220,6 +4220,6 @@ void query_stats_schemas_cb(StatsSchemaList **result, Error **errp)
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if (first_cpu) {
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stats_args.result.schema = result;
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stats_args.errp = errp;
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- run_on_cpu(first_cpu, query_stats_schema_vcpu, RUN_ON_CPU_HOST_PTR(&stats_args));
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+ query_stats_schema_vcpu(first_cpu, &stats_args);
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}
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}
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diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
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index 4871ad85f074..3b765beb9b1c 100644
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--- a/include/hw/core/cpu.h
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+++ b/include/hw/core/cpu.h
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@@ -402,6 +402,7 @@ struct CPUState {
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struct kvm_dirty_gfn *kvm_dirty_gfns;
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uint32_t kvm_fetch_index;
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uint64_t dirty_pages;
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+ int kvm_vcpu_stats_fd;
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/* Use by accel-block: CPU is executing an ioctl() */
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QemuLockCnt in_ioctl_lock;
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