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Date: Thu, 11 Jun 2015 11:31:09 +0200
From: =?windows-1252?Q?Roger_Pau_Monn=E9?= <roger.pau@citrix.com>
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To: Stefan Andritoiu <stefan.andritoiu@gmail.com>,
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Subject: Re: Lock Holder Preemption on bhyve
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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.