On 10/03/21 18:05, Marc Zyngier wrote:
On Wed, 10 Mar 2021 16:03:42 +0000, Paolo Bonzini pbonzini@redhat.com wrote:
On 10/03/21 16:51, Marc Zyngier wrote:
- kvm_for_each_vcpu(j, vcpu, kvm) {
pdata = data + VM_STAT_COUNT;for (i = 0; i < VCPU_STAT_COUNT; i++, pdata++)*pdata += *((u64 *)&vcpu->stat + i);Do you really need the in-kernel copy? Why not directly organise the data structures in a way that would allow a bulk copy using copy_to_user()?
The result is built by summing per-vCPU counters, so that the counter updates are fast and do not require a lock. So consistency basically cannot be guaranteed.
Sure, but I wonder whether there is scope for VM-global counters to be maintained in parallel with per-vCPU counters if speed/efficiency is of the essence (and this seems to be how it is sold in the cover letter).
Maintaining VM-global counters would require an atomic instruction and would suffer lots of cacheline bouncing even on architectures that have relaxed atomic memory operations.
Speed/efficiency of retrieving statistics is important, but let's keep in mind that the baseline for comparison is hundreds of syscalls and filesystem lookups.
Paolo