From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Ostrovsky Subject: Re: [PATCH v6 1/5] sysctl: Make XEN_SYSCTL_numainfo a little more efficient Date: Tue, 07 Apr 2015 12:57:39 -0400 Message-ID: <55240C83.2050803@oracle.com> References: <1428358329-8466-1-git-send-email-boris.ostrovsky@oracle.com> <1428358329-8466-2-git-send-email-boris.ostrovsky@oracle.com> <5523FFF3.8050106@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5523FFF3.8050106@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Andrew Cooper , ian.jackson@eu.citrix.com, ian.campbell@citrix.com, wei.liu2@citrix.com, stefano.stabellini@eu.citrix.com, dgdegra@tycho.nsa.gov, jbeulich@suse.com, keir@xen.org Cc: elena.ufimtseva@oracle.com, dario.faggioli@citrix.com, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On 04/07/2015 12:04 PM, Andrew Cooper wrote: > On 06/04/15 23:12, Boris Ostrovsky wrote: >> A number of changes to XEN_SYSCTL_numainfo interface: >> >> * Make sysctl NUMA topology query use fewer copies by combining some >> fields into a single structure and copying distances for each node >> in a single copy. >> * NULL meminfo and distance handles are a request for maximum number >> of nodes (num_nodes). If those handles are valid and num_nodes is >> is smaller than the number of nodes in the system then -ENOBUFS is >> returned (and correct num_nodes is provided) >> * Instead of using max_node_index for passing number of nodes keep this >> value in num_nodes: almost all uses of max_node_index required adding >> or subtracting one to eventually get to number of nodes anyway. >> * Replace INVALID_NUMAINFO_ID with XEN_INVALID_MEM_SZ and add >> XEN_INVALID_NODE_DIST. >> >> Signed-off-by: Boris Ostrovsky >> Acked-by: Ian Campbell > This subtly changes the behaviour of XEN_SYSCTL_numainfo with regards to > NULL guest handles. > > Previously, a caller was able to select which information they wanted by > choosing which guest handles were non-NULL. > > With the new semantics, the caller must pass both ni->meminfo and > ni->distance to get either bit of information. Each > copy_to_guest_offset() should be gated on a !guest_handle_is_null() so a > caller can request meminfo information without distance information. Currently the caller, in fact, can have either of three pointers (node_to_memsize, node_to_memfree or node_to_node_distance) as NULL and the hypervisor will fill whichever pointer is valid. Because I put the first two together into a struct we are already changing behavior in that regard. Not to mention that having all three as NULL now has new meaning as well. I thought that either both pointers should be valid or neither. If people disagree I can change this. -boris