Re: BUFQ_READPRIO & BUFQ_PRIOCSCAN

[Sevan Janiyan <venture37%geeklan.co.uk@localhost>]

Looks like I was way off. I compared between sysctl & dkctl output
between amd64 & macppc port before I replied to the list & didn't look
at the source code.

On 01/23/18 22:06, Paul Goyette wrote:
> That's not quite 100% true, as I recall.  As I discovered while making
> the various strategies into modules ....
> 
> The ccd, cgd, fss, dkwedge, raidframe, and flash drivers explicitly
> request the "fcfs" bufq strategy (in the call to bufq_alloc()), as does
> the nvme driver (via its call to ldattach()).  The gpib/xxx ct, md, and
> rd drivers also request "fcfs".
> 
> The scsi cd(4) driver explicitly requests the "disksort" strategy.
> 
> The ata/wd, ld, and vnd drivers request BUFQ_SORT_RAWBLOCK
> 
> The scsi sd driver as well as the ata/wd driver and all other callers of
> ldattach() use the default BUFQ_DISK_DEFAULT_STRAT which allows the
> system to pick one based on the priority (and the SORT flag) - see
> kern/subr_bufq.c:bufq_alloc()
> 
> The priority values (higher number preferred) are:
> 
>     fcfs       10
>     disksort   20
>     readprio   30
>     priocscan  40
> 
> The above is not a completely exhaustive list - check all the callers of
> bufq_alloc() for more details, especially WRT machine- and architecture-
> specific devices.


Sevan