Constant load of 1 on a recent 12-STABLE

[Gordon Bergling]

On Thu, Jul 02, 2020 at 10:40:50AM +0300, Andriy Gapon wrote:
> On 23/06/2020 10:23, Gordon Bergling wrote:
> > What is maybe also related to the problem is the following top output, 
> > collected by 'top -HS'. The three zfskern threads generate little load, but that
> > constant. The annoying part of the problem is, that the load of 1 is reported and
> > that the hostsystem schedules the thread over all 4 physical cores and keeps the
> > clockrate at the highest frequency.
> > 
> >   PID USERNAME    PRI NICE   SIZE    RES STATE    C   TIME    WCPU COMMAND
> >    11 root        155 ki31     0B    64K CPU2     2  17:28  97.39% idle{idle: cpu2}
> >    11 root        155 ki31     0B    64K CPU3     3  17:29  96.78% idle{idle: cpu3}
> >    11 root        155 ki31     0B    64K CPU1     1  17:29  96.40% idle{idle: cpu1}
> >    11 root        155 ki31     0B    64K RUN      0  17:25  96.13% idle{idle: cpu0}
> >     8 root         -8    -     0B  1040K mmp->m   2   0:44   4.32% zfskern{mmp_thread_enter}
> >     8 root         -8    -     0B  1040K mmp->m   1   0:44   4.28% zfskern{mmp_thread_enter}
> >     8 root         -8    -     0B  1040K mmp->m   3   0:44   4.25% zfskern{mmp_thread_enter}
> > 
> > Does anyone has some insight where zfskern is spawned? I maybe can bisect then the resulting change
> > which leads to this behaviour.
> 
> That's strange.  Those mmp threads shouldn't really be consuming much CPU.
> Normally they should just sleep all the time.
> Do you use the new ZFS multi-modifier protection feature?  I guess not.
> Do you have 'multihost' property set on any of your pools?
> 
> The change you were looking for is
> r361383 MFC r354804,r354806,r354807,r354885: 10499 Multi-modifier protection (MMP)

I didn't use the ZFS multi-modifier protection feature and didn't have the 'multihost'
propery set on any of my 3 ZFS pools. Thanks for identifing the particular change. I
have tried OpenZFS from ports, which seems to improve the situation, but I went back
to the base version since only the zroot pool was found and the two others pools 
weren't detected.

--Gordon

> -- 
> Andriy Gapon