decouple maximum clock frequency from callout scheduling granularity
AbandonedPublic
Actions

Authored by kmacy on Nov 27 2015, 12:28 AM.

Details

Reviewers

Summary

Motivated by the need to schedule retransmits at a granularity less than 1ms while not swamping the CPU with excess timer interrupts.

change ticks to long
add a separate hardclock frequency: kern.hardclock_hz
make callout precision behave sensibly, where value passed is 0 or less than SBT_1US it gets replaced with sbt corresponding to hardclock_hz (SBT_1MS by default)
add tvtohz64
replace calls likely to wrap at higher frequency with tvtohz64

Diff Detail

Repository

rS FreeBSD src repository - subversion

Lint

Lint Skipped

Unit

Tests Skipped

Event Timeline

kmacy updated this revision to Diff 10533.Nov 27 2015, 12:28 AM

kmacy retitled this revision from to decouple maximum clock frequency from callout scheduling granularity.

kmacy updated this object.

kmacy edited the test plan for this revision. (Show Details)

kmacy added a reviewer: davide.

kmacy set the repository for this revision to rS FreeBSD src repository - subversion.

Herald added a subscriber: imp. · View Herald TranscriptNov 27 2015, 12:28 AM

kmacy added a project: transport.Nov 27 2015, 12:42 AM

kmacy added a subscriber: benno.

The changes look good. I'd split them in multiple patches/commit, more or less following the structure you outlined in the summary, but thanks for sending out a single one so we can have the whole picture.
IIRC there were objections to change ticks from 32-bits to 64-bits so you may want to ask feedback from a more general audience.
Other than that, I'm fine with (a splitted version of this) getting in.

sys/kern/kern_clock.c
472	Atomic on 64-bit integers are slightly more expensive than the 32-bit counterparts. I think it's fine, but do we have numbers on what's the impact of this? (maybe profiling).
sys/kern/kern_tc.c
1285	I may miss something here, but do you ever use the value of the counter you just read?
sys/kern/kern_timeout.c
597	Please add a comment specifying why you round-up, for clarity.
957	Can this be KASSERT() maybe with a message attached "precision needs to be at least 1US"? I'm not fussed about it, so if you don't like it you can leave it as is.
sys/kern/subr_param.c
88	I think you ate a whitespace two lines below.
116	Nit: SYSCTL descriptions always start with capital letters, can you change that?
sys/sys/callout.h
61	Nit again, this seems unaligned.