Re: [Libvir] PATCH: Improve performance on Xen

The Xen implementations of virDomainLookupByID virDomainLookupByUUID virDomainLookupByName virDomainGetOSType all have sub-optimal performance since they speak to XenD. The lookupXXX functions all basically require 3 pieces of info in the end (name,id,uuid). They each get given one piece & have to lookup the other piece. Every running domain has to have an entry in XenStore on /local/domain/N where 'N' is the id. Under this location there is always a 'name' field. So if we have the id we can efficiently get the name. I just realized that the getdomaininfo hypercall struct contains the uuid and id. So for the ByID and ByUUID calls we can get all the info we need with a hypercall and a read of xenstore. This is very efficient compared to hitting XenD. As of Xen 3.1.0 hypervisor the flags in the getdomaininfo hypercall struct also mark whether the guest is HVM vs paraivrt, so we can also implement the GetOSType api with a single hypercall. That just leaves the ByName impl. The only way I can think of doing this is to scan /local/domain/N in xenstore until we find it. I'm going to try this, but I'm not convinced it'll be any significantly than talking to XenD. I may be surprised though. Any for the 3 improvements I have done, the 'virsh dominfo' call has improved when using either ID or UUID: Create a set of UUIDs & IDs # for i in `seq 1 500` ; do echo dominfo 73 ; done > ids.txt # for i in `seq 1 500` ; do echo dominfo 8f07fe28-753f-2729-d76d-bdbd892f949a ; done > uuids.txt Now before measurements: # time ./virsh < ids.txt > /dev/null real 0m17.317s user 0m0.144s sys 0m0.164s # time ./virsh < uuids.txt > /dev/null real 0m14.432s user 0m0.236s sys 0m0.460s Against the after measurements: # time ./virsh < demo.txt > /dev/null real 0m0.259s user 0m0.100s sys 0m0.072s # time ./virsh < demo.txt > /dev/null real 0m0.482s user 0m0.324s sys 0m0.108s A pretty good speedup really considering how frequently these calls are made if you're monitoring domains frequently.