From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [PATCH v6 1/5] sysctl: Make XEN_SYSCTL_numainfo a little more efficient Date: Mon, 13 Apr 2015 16:52:21 +0100 Message-ID: <552C02550200007800071973@mail.emea.novell.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> <55240C83.2050803@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <55240C83.2050803@oracle.com> Content-Disposition: inline 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.campbell@citrix.com, wei.liu2@citrix.com, ian.jackson@eu.citrix.com, stefano.stabellini@eu.citrix.com, Boris Ostrovsky , dgdegra@tycho.nsa.gov, 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 07.04.15 at 18:57, wrote: > 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. I agree with Andrew's view, fwiw. Jan