Hi Roger

Thank you for the links, I have been looking for more information on
Paravirtualized ticket spinlocks for a later project.
I know how Xen handles LHP, but it does so through what are called
"invasive methods", that modify the guest.
For now, my work focuses on a non-invasive methods in which the guest
is not aware that it is a guest. In hopes to offer a solution to LHP,
regardless of the guest OS.

Thank you,

On Thu, Jun 11, 2015 at 12:31 PM, Roger Pau Monné <roger....@citrix.com> wrote:
> Hello,
> El 06/06/15 a les 0.59, Stefan Andritoiu ha escrit:
>> Hello everyone,
>> My name is Stefan Andritoiu and I'm currently studying Computer
>> Science in my 4th year at the University POLITEHNICA of Bucharest.
>> I'm fairly new to the FreeBSD operating system, having only a
>> background in Linux. For the past few months I've been investigating
>> the problem of Lock Holder Preemption on bhyve, how other hypervisors
>> deal with this problem and a possible implementation of these
>> solutions on bhyve.
>> I am currently working on implementing Gang Scheduling on FreeBSD to
>> test if it is a viable solution. I also plan to continue my work, by
>> implementing and testing other techniques of avoiding overhead caused
>> by lock holder preemption, and comparing their results.
> FWIW, Xen doesn't do gang-scheduling, so the lock-holder preemption
> problem is solved inside of the guest by using
> pvspinlocks/pvticketlocks. Not to detriment the work you are doing on
> gang-scheduling, but having some like this would help FreeBSD when
> running in all virtualized environments regardless of whether the
> underlying hypervisor does gang-scheduling or not. Some more information
> about it:
> https://blog.xenproject.org/2012/05/11/benchmarking-the-new-pv-ticketlock-implementation/
> http://www-archive.xenproject.org/files/xensummitboston08/LHP.pdf
> https://lwn.net/Articles/556141/
> Roger.
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