https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=221956
Bug ID: 221956
Summary: cam iosched: Schedule cam_iosched_ticker() quanta
times per second
Product: Base System
Version: CURRENT
Hardware: Any
OS: Any
Status: New
Keywords: patch
Severity: Affects Some People
Priority: ---
Component: kern
Assignee: freebsd-bugs@FreeBSD.org
Reporter: f...@fabiankeil.de
Flags: mfc-stable11?
Created attachment 185947
--> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=185947&action=edit
cam iosched: Schedule cam_iosched_ticker() quanta times per second
The attached patch lets cam iosched schedule cam_iosched_ticker()
quanta times per second
According to callout_reset(9), "[w]hen ticks is used, the callout is
scheduled to execute after ticks/hz seconds".
It follows that to get quanta calls per second one should specify
a tick value of hz / isc->quanta.
Previously the value was additionally reduced by one.
As a result cam_iosched_ticker() was called more often than
requested by the user and expected by some of the limiters.
On a system with hz=1000 a quanta value of 200 resulted in 250
calls and a value of 100 in 111 calls.
Without the unexplained tick reduction the number of calls matches
the quanta value reasonably well.
Obtained from: ElectroBSD
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