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Subject: Re: [hwloc-devel] hwloc with Xen system support - some initial code
From: Brice Goglin (Brice.Goglin_at_[hidden])
Date: 2014-01-06 09:10:36


Hello,

Here's a new patchset that fixes the remaining problems on my side.
01 is basically the same I sent earlier.
02 and 03 export two core functions to plugins
04 is basically the same I sent earlier, without the hacky #include
<private/private.h> that was waiting for 02-03
05 lets me check that topology-xen.c builds when libxen isn't available
(useful for regression testing all backends when changing internals,
used with "make check -C tests/ports")

The Xen component seems to work fine as a plugin. The Xen lib dependency
is only in the plugin:
$ ldd utils/.libs/lstopo | grep xen
$ ldd src/.libs/libhwloc.so | grep xen
$ ldd src/.libs/hwloc_xen.so | grep xen
    libxenctrl-4.3.so => /usr/lib/libxenctrl-4.3.so (0x00007f3de693c000)

You can try with
    make && make install && HWLOC_XEN=1 utils/lstopo
Add HWLOC_PLUGINS_VERBOSE for details about plugins being loaded. And
HWLOC_COMPONENTS_VERBOSE for details components being enabled or not.

A couple comments below.

Le 01/01/2014 22:47, Andrew Cooper a écrit :
> At the moment, my list of activities is:
> * See about getting plugins working (./configure is still wanting to
> build Xen support in, rather than making it a plugin)
> * Get NUMA memory and distances recorded (as the information is already
> available)
> * Get offline cpus working.
>
> I am in two minds about that patch to libxc.
>
> On the one hand, libxenctrl is a fairly lightweight library (no
> dependencies), whose purpose is to be a thin wrapper to basic Xen
> controls. However, it explicitly has an unstable API which is free to
> change in the future, and I can make no guarentee that the API of those
> functions wont change (especially as I have a plan to remove the
> ambiguity between online/offline cpus and their topology location).

Is there a #define that we check to easily detect which API is available
without having multiple API checks in configure?

> The other option which I discounted initially was to use libxenlight.
> libxl explicitly has a stable API (but unstable ABI). It comes with a
> host of dependencies (libxlutil, libxenstore, libxenguest, libyajl,
> libuuid, libbz2, liblzma, libz off the top of my head, and probably more).

According to you, in reality, how often will libxl be installed on
existing platforms, compared to libxc?

> Furthermore, libxc exported the information in the format I wanted to
> consume it in, rather than libxl which translates it to a less useful
> format as part of retrieving the information.
>
> As the Xen part of hwloc is going to be a plugin, using libxl might not
> be so bad, and having a stable API would certainly be good (even if it
> means doing a reverse transform on the information received from libxl).

We won't release hwloc v1.9 before a couple months. You can take some
time to decide. I don't have a strong feeling about this choice.

Brice