Re: priocscan vs fcfs

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

On Thu, 3 Dec 2015, Petar Bogdanovic wrote:
> On Wed, Dec 02, 2015 at 08:23:28PM +0000, Michael van Elst wrote:
> > That's probably why setting the queues all to fcfs is the best
> > for you.
>
> Not as dramatic as Emile's numbers but significantly higher read
> throughput:

Am I missing something here? Your figures suggest that Input (i.e. 
reading) is pretty much the same, but it is Output (i.e. writing) that 
has higher throughput

>    # for i in disksort fcfs priocscan; do
>        for j in wd0 wd1 raid0; do dkctl $j strategy $i; done;
>            bonnie++ -d /tmp -m $i -s 4g -n 0 -u build -f -D; done
>
>    /dev/rwd0d: disksort -> disksort
>    /dev/rwd1d: disksort -> disksort
>    /dev/rraid0d: disksort -> disksort
>    (...)
>    Version  1.97       ------Sequential Output------ --Sequential Input- --Random-
>    Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
>    Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
>    disksort         4G           33550  13 25694   8           64922  13 238.2  11
>    Latency                        1023ms     309ms               161ms    4111ms
>
>    /dev/rwd0d: disksort -> fcfs
>    /dev/rwd1d: disksort -> fcfs
>    /dev/rraid0d: disksort -> fcfs
>    (...)
>    Version  1.97       ------Sequential Output------ --Sequential Input- --Random-
>    Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
>    Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
>    fcfs             4G           55254  22 27584   9           64438  13 244.5   9
>    Latency                         844ms     331ms               233ms    6095ms
>
>    /dev/rwd0d: fcfs -> priocscan
>    /dev/rwd1d: fcfs -> priocscan
>    /dev/rraid0d: fcfs -> priocscan
>    (...)
>    Version  1.97       ------Sequential Output------ --Sequential Input- --Random-
>    Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
>    Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
>    priocscan        4G           32649  13 17028   6           60478  13 247.6   8
>    Latency                        1983ms    1167ms               236ms    6198ms
>
>
> That's on a simple RAID1 setup:
>
>    # dmesg | grep SAM
>    wd0: <SAMSUNG HD154UI>
>    wd1: <SAMSUNG HD154UI>
>
>    # mount | grep raid
>    /dev/raid0a on / type ffs (log, NFS exported, local)