CAM I/O Scheduler (was Re: FreeBSD Quarterly Status Report - First Quarter 2016 (fwd))

Warner Losh wlosh at
Tue May 3 15:25:31 UTC 2016

> On May 3, 2016, at 8:05 AM, Warren Block <wblock at> wrote:
> On Tue, 3 May 2016, Johan Hendriks wrote:
>> Op 02/05/16 om 02:49 schreef Warren Block:
>>      CAM I/O Scheduler
>>         Links
>>         I/O Scheduling in FreeBSD's CAM Subsystem (PDF) URL:
>>         The BSDCan 2015 Talk URL:
>>         Contact: Warner Losh <wlosh at>
>>         An enhanced CAM I/O scheduler has been committed to the tree. By
>>         default, this scheduler implements the old behavior. In addition, an
>>         advanced adaptive scheduler is available. Along with the scheduler,
>>         SATA disks can now use Queued Trims with devices that support them.
>>         Details about the new scheduler are available in the I/O Scheduling in
>>         FreeBSD's CAM Subsystem article (PDF) or from the BSDCan 2015 talk.
>> I updated my source today, but CAM_ADAPTIVE_IOSCHED yields an error about an unknown option.
>> If I use CAM_NETFLIX_IOSCHED the kernel compiles.
> That is my understanding, yes.  Warner can certainly explain it better than I can, so CCed.

I’m changing it to CAM_ADAPTIVE_IOSCHED, but haven’t yet due to “work flow” issues
in making sure that the Netflix repo doesn’t see a large number of conflicts when this
is merged. I’ll see if I can finish today, but CAM_NETFLIX_IOSCHED is the old name.


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