pw operations slow under zfs load

[Karl Denninger]

On 7/29/2015 16:13, javocado wrote:
> Sorry, the boot disk (SSD) is plain old ufs.
>
> On Wed, Jul 29, 2015 at 2:11 PM, javocado <javocado at gmail.com> wrote:
>
>> Hi,
>>
>> We have a pretty busy ZFS pool running on an 8.3 AMD system. We are
>> noticing that when the pool is busy pw-related operations seem to  take a
>> long time to complete:
>>
>> # time pw unlock 1000
>> 0.007u 0.036s 0:39.72 0.0%      45+1953k 0+113io 0pf+0w
>>
>> # time pw lock 1000
>> 0.032u 0.022s 1:09.63 0.0%      24+1132k 0+114io 0pf+0w
>>
>> Wile the command is running, we note that the process is locked in the D
>> state:
>>
>> root  85051  0.0  0.0  5832   960   0  D+    1:53PM   0:00.02
>> /usr/sbin/pwd_mkdb -u 1000 /etc/master.passwd
>>
>> We also note that there is next to 0 disk activity on the boot volume:
>>
>> # gstat -f ad
>>
>> dT: 1.005s  w: 1.000s  filter: ad
>>  L(q)  ops/s    r/s   kBps   ms/r    w/s   kBps   ms/w   %busy Name
>>     0      0      0      0    0.0      0      0    0.0    0.0| ad6
>>     0      0      0      0    0.0      0      0    0.0    0.0| ad8
>>     0      0      0      0    0.0      0      0    0.0    0.0| ad10
>>     0      0      0      0    0.0      0      0    0.0    0.0| ad12
>>
>> And plenty of free mem:
>>
>> Mem: 400M Active, 3391M Inact, 128G Wired, 1935M Cache, 14G Buf, 6055M Free
>>
>> So, what's going on here? How does a busy pool with it's own set of drives
>> (which operate off an HBA) affect the speed of operations involving the
>> boot volume (an SSD connected to the mobo)?
>>
>>
>>
A very common manifestation of the way ZFS and the VM system interact,
unfortunately.

It's better in 9.x and 10.x, and the patch I have against them makes it
even better, but it still isn't completely resolved.

-- 
Karl Denninger
karl at denninger.net <mailto:karl at denninger.net>
/The Market Ticker/
/[S/MIME encrypted email preferred]/
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