[openib-general] [PATCH] use mmiowb after doorbell ring

[Roland Dreier]

 > > > Hopefully that is under prefix:
 > > > $prefix/etc/libibverbs.conf.d/
 > > 
 > > Well, $sysconfdir/libibverbs.conf.d
 > 
 > Ugh, is that a problem if I want to build and run as non-root?
 > I'm used to be able to set --prefix on config line for all libs
 > to some directory, put LD_LIBRARY_PATH to point there, then
 > if I like I just blow all of it away and I get a clean system.
 > Scattering config files around in home directory etc will break this.

I'm not following the objection: what's wrong with using $sysconfdir?
It defaults to $prefix/etc like you want, and it can be overridden
with the --sysconfdir parameter to configure.

 > > > Finally, it might be nice to be able to just specify the list of
 > > > plugins at configure time for people like me who buuild everything
 > > > from source and who want less flexibility
 > > > but also less files to install.
 > > 
 > > Again, is that really any easier
 > 
 > Well, I'm thinking of distributed systems mainly where copying extra
 > files around is additional pain.
 > Consider myself: I'm building things on my laptop, then pushing them out to
 > machines in the lab over rsync for testing. Less files - less headache.
 > 
 > > than putting whatever you want into
 > > your .libibverbs.conf?
 > 
 > I really don't think a library sticking things in user's home directory
 > is such a great idea - typical users don't really know they link against
 > some library, this is just an extra place that users can break:
 > move to another machine, things stop working, and your app's
 > manual does not say anything of course.

libraries don't stick anything in home directories -- I'm just
suggesting $HOME/.libibverbs.conf as a place to stick extra configs
that users might want to add.

I'm kind of thinking that we might want other config options beyond
just driver names someday.  Otherwise we might as well have
/etc/libibverbs.drivers.d and an environment variable IBV_DRIVERS, I
guess.  But it might be nice to be able to add a line like

    default-fork-safe true

somewhere in libibverbs.conf.d to set a system-wide default.

I dunno what's better.  Maybe separate environment variables for
user-specific configs are just as good -- eg that's what ld.so does.

 > 
 > > I definitely plan to make it so a missing plug-in is not fatal, so it
 > > shouldn't hurt to have extra drivers declared that you don't build
 > > every time.
 > 
 > Not until someone decides to rename a plugin for some reason - then you have to
 > hunt down and kill the old file name to prevent an old version stuck in library
 > path for some reason from being loaded - easy with the central location, but
 > good luck walking all user's home directories.

Hmm, this seems to argue against allowing environment variables or
anything but a single directory built into libibverbs.  Because
otherwise you have to grep every .bashrc .cshrc and so on.

 - R.