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[PULL 06/18] kvm: reuse per-vcpu stats fd to avoid vcpu interruption
From: |
Paolo Bonzini |
Subject: |
[PULL 06/18] kvm: reuse per-vcpu stats fd to avoid vcpu interruption |
Date: |
Mon, 26 Jun 2023 13:14:33 +0200 |
From: Marcelo Tosatti <mtosatti@redhat.com>
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 <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
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;
--
2.41.0
- [PULL 00/18] Misc, i386 patches for 2023-06-26, Paolo Bonzini, 2023/06/26
- [PULL 03/18] numa: Validate cluster and NUMA node boundary if required, Paolo Bonzini, 2023/06/26
- [PULL 04/18] hw/arm: Validate cluster and NUMA node boundary, Paolo Bonzini, 2023/06/26
- [PULL 01/18] build: further refine build.ninja rules, Paolo Bonzini, 2023/06/26
- [PULL 02/18] hw/remote/proxy: Remove dubious 'event_notifier-posix.c' include, Paolo Bonzini, 2023/06/26
- [PULL 06/18] kvm: reuse per-vcpu stats fd to avoid vcpu interruption,
Paolo Bonzini <=
- [PULL 05/18] hw/riscv: Validate cluster and NUMA node boundary, Paolo Bonzini, 2023/06/26
- [PULL 07/18] target/i386: fix INVD vmexit, Paolo Bonzini, 2023/06/26
- [PULL 08/18] target/i386: TCG supports 3DNow! prefetch(w), Paolo Bonzini, 2023/06/26
- [PULL 09/18] target/i386: TCG supports RDSEED, Paolo Bonzini, 2023/06/26
- [PULL 10/18] target/i386: do not accept RDSEED if CPUID bit absent, Paolo Bonzini, 2023/06/26
- [PULL 11/18] target/i386: TCG supports XSAVEERPTR, Paolo Bonzini, 2023/06/26
- [PULL 13/18] target/i386: Intel only supports SYSCALL/SYSRET in long mode, Paolo Bonzini, 2023/06/26
- [PULL 12/18] target/i386: TCG supports WBNOINVD, Paolo Bonzini, 2023/06/26
- [PULL 16/18] target/i386: implement RDPID in TCG, Paolo Bonzini, 2023/06/26
- [PULL 14/18] target/i386: AMD only supports SYSENTER/SYSEXIT in 32-bit mode, Paolo Bonzini, 2023/06/26