Re: [Xen-devel] [PATCH v2 2/4] sysctl: Make XEN_SYSCTL_topologyinfo sysctl a little more efficient

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.01.15 at 17:16, <Ian.Campbell@xxxxxxxxxx> wrote:
> On Fri, 2015-01-16 at 16:06 +0000, Jan Beulich wrote:
>> >>> On 16.01.15 at 16:56, <boris.ostrovsky@xxxxxxxxxx> wrote:
>> > On 01/07/2015 04:12 AM, Jan Beulich wrote:
>> >>>>> On 06.01.15 at 14:41, <andrew.cooper3@xxxxxxxxxx> 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 <boris.ostrovsky@xxxxxxxxxx>
>> >>> 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)
>> >> In which case leaving the sysctl alone and just adding a new non-sysctl
>> >> interface should be considered.
>> > 
>> > (Sorry for late reply)
>> > 
>> > Would a platform op be an option here or do you prefer a whole new 
>> > hypercall?
>> 
>> From an abstract pov a platform op would be fine, but iirc you had
>> a need for preempting, which doesn't work well for that hypercall.
>> A whole new one seems overkill too. Perhaps slightly bending what
>> physdevop-s are used for might be an option...
> 
> Unlike sysctls, physdevop-s are exposed to/stable for dom0 too aren't
> they?

Sure, just like platformop-s. What is it I'm not understanding you
try to point out with your question?

Jan


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