Re: [libvirt] [RFC][scale] new API for querying domains stats

Hi Richard, Thanks for your comment! On 08/04/2014 04:39 PM, Richard W.M. Jones wrote: > On Mon, Aug 04, 2014 at 11:38:41AM +0800, Li Wei wrote: >> Hi, >> >> On 07/22/2014 03:25 PM, Richard W.M. Jones wrote: >>> >>> Did anything come of this discussion, and/or is someone working on this? >> >> I am working on an API to query block stats in a bulk style and proposed an >> API as follow: >> >> virDomainBlockStatsBulkFlags(virDomainPtr dom, >> virTypedParameterPtr params, >> int nparams, >> int ndisks, >> unsigned int flags) >> >> @dom: pointer to domain object >> @params: an array of typed param to be populated with block stats >> @nparams: how many params used for each block device >> @ndisks: how many block devices to query >> @flags: flags to filter block devices (not used for now) >> >> Returns -1 in case of error, 0 in case of success. >> with params == NULL, nparams == -1, ndisks == 1, return number of params for each block device. >> with params == NULL, nparams == -1, ndisks == -1, return number of disks in the domain. >> >> A typical usage of this API should be: >> nparams = virDomainBlockStatsBulkFlags(dom, NULL, -1, 1, 0); >> ndisks = virDomainBlockStatsBulkFlags(dom, NULL, -1, -1, 0); >> >> params = VIR_ALLOC_N(params, nparams * ndisks); >> >> ret = virDomainBlockStatsBulkFlags(dom, params, nparams, ndisks, 0); >> >> ... do something with params >> >> VIR_FREE(params); >> >> With this bulk API, virt-top can updates in a short interval for a domain with a lot of disks. >> Any comments? > > I think this works OK for the case where you have 1 domains with > lots of disks. > > However if you have a large number of domains each with 1 or 2 > disks I think you would have the same problem as currently. Yes, it is. > > Is it possible to design an API that can work across all domains > in a single call? How about the following API: int virConnectGetAllBlockStats(virConnectPtr conn, virDomainPtr domain, virDomainBlockBulkStatsPtr *stats, unsigned int flags); @conn: pointer to libvirt connection @domain: pointer to the domain to be queried, NULL for all domains @stats: array of virDomainBlockBulkStats struct(see below) to be populated @flags: filter flags

Return the number of virDomainBlockBulkStats populated. where virDomainBlockBulkStats defined as: struct _virDomainBlockBulkStats { virDomainPtr domain; /* domain the block stats belongs to */ virTypedParameterPtr params; /* params to store block stats */ unsigned int nparams; /* how many params used for each block stats */ unsigned int ndisks; /* how many block stats in this domain */ }; Note: 1. because the API allocate memory to store stats, the caller need to free it after use. 2. to distinguish each block stats in a domain, we need use a param to store block device name. > >> PS: >> It seems we need a bunch of bulk APIs to query stats, I wonder if I can submit a patchset for each >> bulk API or must supply all the bulk APIs in one patchset? > > Whichever is easiest to review. I suspect that smaller patches, each > containing a single new API, will be simpler to review, but that's > just my opinion. I prefer this way also. Thanks, Li Wei > > Rich. > -- libvir-list mailing list libvir-list(a)redhat.com https://www.redhat.com/mailman/listinfo/libvir-list .