Re: measuring swap partition speed

Van: void <void@f-m.fm>
Datum: vrijdag, 22 december 2023 01:05
Aan: freebsd-fs <freebsd-fs@freebsd.org>
Onderwerp: Re: measuring swap partition speed
> 
> On Thu, 21 Dec 2023, at 18:56, Ronald Klop wrote:
> > A bit weird that a simple dd is so slow.
> >
> > Just a quick thought.
> > Are your partitions aligned properly?
> 
> no idea. How would I check? The system when installed,
> the auto-zfs option was selected, block size set to 4k. The swap
> was changed from the default 2gb to 12gb. geli encryption is
> active for the zfs filesystem but not for swap. It's only the swap
> that shows performance issues.
> 
> > Is other IO going on on the same time?
> 
> not really, the tests were done with cron jobs deactivated, almost completely idle,
> swap was not being used at all.
> 
> > What does gstat say about %util, queue length and all the other stats
> > while running the dd? Or "iostat -x -d 1".
> 
> I'll try that next, thanks
> 
> > Could you try if another disk has the same issues?
> 
> no spare or equivalent disk for this arch.
> 
> > How is your disk connected? USB-to-SATA-adapter? Any output of dmesg?
> 
> Regular usb3 connection.
> 
> da0: 400.000MB/s transfers
> da0: 953869MB (1953525168 512 byte sectors)
> da0: quirks=0x2<NO_6_BYTE>
> da0: Delete methods: <NONE(*),ZERO>
> -- 
>  
> 
> 
> 


Can you provide more concrete information? Like:

# usbconfig list
ugen0.1: <(0x1106) XHCI root HUB> at usbus0, cfg=0 md=HOST spd=SUPER (5.0Gbps) pwr=SAVE (0mA)
ugen0.2: <vendor 0x2109 USB2.0 Hub> at usbus0, cfg=0 md=HOST spd=HIGH (480Mbps) pwr=SAVE (100mA)
ugen0.3: <Silicon Labs CP2102 USB to UART Bridge Controller> at usbus0, cfg=0 md=HOST spd=FULL (12Mbps) pwr=ON (100mA)
ugen0.4: <USB 3.0 Device USB 3.0 Device> at usbus0, cfg=0 md=HOST spd=SUPER (5.0Gbps) pwr=ON (224mA)
ugen0.5: <Western Digital Elements 25A2> at usbus0, cfg=0 md=HOST spd=SUPER (5.0Gbps) pwr=ON (224mA)

And the output of "devinfo -v". That will give people much more information to work with instead of "anecdotal evidence" about your hardware being usb3.
And the complete output of dmesg instead of only the "da0:" lines. There is more information in there which can be valuable for people to help you.

About the alignment. You wrote in your first mail:
"# gpart show

=>        40  1953525088  da0  GPT  (932G)
           40      532480    1  efi  (260M)
       532520        2008       - free -  (1.0M)
       534528     4194304    2  freebsd-swap  (2.0G)
      4728832     4194304    4  freebsd-swap  (2.0G)
      8923136     4194304    5  freebsd-swap  (2.0G)
     13117440     4194304    6  freebsd-swap  (2.0G)
     17311744     4194304    7  freebsd-swap  (2.0G)
     21506048     4194304    8  freebsd-swap  (2.0G)
     25700352  1927823360    3  freebsd-zfs  (920G)
   1953523712        1416       - free -  (708K)
"

Your dd tests were on da0p4 which starts on block 4728832.
Assuming "gpart list" shows "Sectorsize: 512".
(4728832 * 512) mod 4096 = 0, so the partitiion is aligned on a 4KB page size. And the calculation is also 0 for 8KB (is this the page size of arm64?) which is good.
AFAIK: this is properly aligned such that the hardware does not need to double write or read-before-write when paging out.

Up until now I haven't seen anything which would explain the slow dd speed on of=/dev/da0p4 vs the quick dd on of=/mnt/test8k.bin.

Regards,
Ronald.