First step for dynticks in FreeBSD

First step for dynticks in FreeBSD Tsuyoshi Ozawa Univ. of Tsukuba ozawa@softlab.cs.tsukuba.ac.jp ozawa@t-oza.net AsiaBSDcon March 14th, 2010 Work-In-Progress talk

Ticks HZ HZ time • Timer interrupt is important processing to work kernel correctly • But it is very expensive to handle periodic ticks

Dynticks time when next Timer is going to be ﬁred • Timer interrupts are generated by using oneshot timer. • This feature is implemented in Solaris, Linux and etc.

Beneﬁts • If OSes can skip needless ticks... • Save power consumption • OS in Virtual Machine work more lightly (e.g. FreeBSD as guest OS) VMware, “Timekeeping in VMware Virtual Machines”, http:// www.vmware.com/pdf/vmware_timekeeping.pdf, 2008

Suggestion • Dynamic Ticks in FreeBSD

Rough Design • Switch mode between periodic tick mode & dynamic tick mode • The switch trigger is when to be scheduled sched_idletd • This function only works when CPU is idle • If the cpu is idle, the CPU has no need to know what current time is. • Scan callout queue & get next event

2 tick mode transition after sched_idletd is scheduled time HZ HZ HZ when next Timer is going to be ﬁred Periodic tick mode Dynamic tick mode • The idle process( sched_idletd ) trigger the mode transition

Current status • Started to write code 11th March, 2010(JST) • I implemented to scan callout queue The routine scan when the next timer event come up?

Wrapping up • I started to implement tickless kernel in FreeBSD. • As ﬁrst step, I implemented the routine which detect when the next timer ﬁre.

Acknowledgements Thanks • Alexander Mortin • Hiroki Sato for advising me !! Any idea or question?

First step for dynticks in FreeBSD

by Tsuyoshi Ozawa on Mar 14, 2010

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First step for dynticks in FreeBSD — Presentation Transcript