Re: [libvirt] [PATCH 0/3] Introduce RW locks to virDomainObjList
On 07/23/2017 02:10 PM, John Ferlan wrote:
On 07/19/2017 10:31 AM, Michal Privoznik wrote:
> While this is not that critical (hash tables have O(1) time complexity for
> lookups), it lays down path towards making virDomainObj using RW locks instead
> of mutexes. Still, in my limited testing this showed slight improvement.
>
> Michal Privoznik (3):
> virthread: Introduce virRWLockInitPreferWriter
> virobject: Introduce virObjectRWLockable
> virdomainobjlist: Use virObjectRWLockable
>
> src/conf/virdomainobjlist.c | 24 ++++----
> src/libvirt_private.syms | 4 ++
> src/util/virobject.c | 144 ++++++++++++++++++++++++++++++++++----------
> src/util/virobject.h | 16 +++++
> src/util/virthread.c | 35 +++++++++++
> src/util/virthread.h | 1 +
> 6 files changed, 180 insertions(+), 44 deletions(-)
>
This could be a "next step" in the work I've been doing towards a common
object:
Sure. If we have just one common object the change can be done in one
place instead of many. I don't care in what order are the changes merged.
https://www.redhat.com/archives/libvir-list/2017-June/msg00916.html
which moves all those driver/vir*obj list API's for Lookup, Search,
ForEach, Add, Remove, etc. into object code since they're essentially
all following the same pattern.
Once there - altering the Lockable lock under the covers should be
relatively simple. I would be called a ListLock or HashLock instead of
an RWLock and the implementation is such that it's R or W depending on
API. Taking a quick refresher look at the series, for a new object I
call virObjectLookupHashClass - that could be the integration point to
use a local initialization for the class and then the appropriate lock
style depending on API.
I think I still prefer "RWLock" name over "ListLock" or
"HashLock" since
its name clearly suggests its purpose. I mean, ListLock doesn't say it's
an RW lock. Moreover, as I say in the cover letter, I'd like to use RW
locks for virDomainObj one day (for instance, there's no reason why two
clients cannot fetch XML for the same domain at the same time).
Therefore, it looks correct to me to derive virDomainObjClass from
virObjectRWLockable instead of ListLock or HashLock or something.
Just thinking off the cuff and of course trying to keep stuff I've been
working on fresh ;-)
Sure, the more recent some patches are the more I understand them. Same
here :-)
Michal