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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.
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>
This commit is contained in:
Marcelo Tosatti 2023-06-18 23:24:40 +02:00 • committed by Paolo Bonzini
parent 3d9981cde9
commit 3b6f485275
2 changed files with 16 additions and 15 deletions
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1
include/hw/core/cpu.h
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@ -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;