From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [PATCH v2 2/4] sysctl: Make XEN_SYSCTL_topologyinfo sysctl a little more efficient Date: Wed, 07 Jan 2015 15:23:36 +0000 Message-ID: <54AD5D88020000780005260B@mail.emea.novell.com> References: <1420510737-22813-1-git-send-email-boris.ostrovsky@oracle.com> <1420510737-22813-3-git-send-email-boris.ostrovsky@oracle.com> <54ABE613.2090608@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <54ABE613.2090608@citrix.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 Cc: wei.liu2@citrix.com, ian.campbell@citrix.com, stefano.stabellini@eu.citrix.com, dario.faggioli@citrix.com, ian.jackson@eu.citrix.com, xen-devel@lists.xen.org, ufimtseva@gmail.com, keir@xen.org, Boris Ostrovsky List-Id: xen-devel@lists.xenproject.org >>> On 06.01.15 at 14:41, wrote: > On 06/01/15 02:18, Boris Ostrovsky wrote: >> Instead of copying data for each field in xen_sysctl_topologyinfo separately >> put cpu/socket/node into a single structure and do a single copy for each >> processor. >> >> There is also no need to copy whole op to user at the end, max_cpu_index is >> sufficient >> >> Rename xen_sysctl_topologyinfo and XEN_SYSCTL_topologyinfo to reflect the > fact >> that these are used for CPU topology. Subsequent patch will add support for >> PCI topology sysctl. >> >> Signed-off-by: Boris Ostrovsky > > If we are going to change the hypercall, then can we see about making it > a stable interface (i.e. not a sysctl/domctl)? There are non-toolstack > components which might want/need access to this information. (i.e. I am > still looking for a reasonable way to get this information from Xen in > hwloc) Now having mentioned the alternative of doing this via other than sysctl several times, I started wondering why exactly we'd want this: hwloc is still user mode code, i.e. whether you call this part of "the toolstack" is ambiguous. The only real reason to make an interface like this other than a sysctl would be if the kernel had a need to access it. The stability of the interface otoh has no meaning here at all imo. We could declare a particular sysctl as "will never change", but I understand that the need to pass the correct XEN_SYSCTL_INTERFACE_VERSION into the hypercall would still make it a little cumbersome to use. Jan