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

Warren Block wblock at
Tue May 3 14:06:02 UTC 2016

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.


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