Single-threaded bottleneck in geli

[Paweł Jakub Dawidek]

Hi Alan,

why do you think it will hurt single-threaded performance?

-- 
Paweł Jakub Dawidek



> On Jul 3, 2020, at 12:30, Alan Somers <asomers at freebsd.org> wrote:
> 
> I'm using geli, gmultipath, and ZFS on a large system, with hundreds of
> drives.  What I'm seeing is that under at least some workloads, the overall
> performance is limited by the single geom kernel process.  procstat and
> kgdb aren't much help in telling exactly why this process is using so much
> CPU, but it certainly must be related to the fact that over 15,000 IOPs are
> going through that thread.  What can I do to improve this situation?  Would
> it make sense to enable direct dispatch for geli?  That would hurt
> single-threaded performance, but probably improve performance for highly
> multithreaded workloads like mine.
> 
> Example top output:
>  PID USERNAME    PRI NICE   SIZE    RES STATE    C   TIME    WCPU COMMAND
>   13 root         -8    -     0B    96K CPU46   46  82.7H  70.54%
> geom{g_down}
>   13 root         -8    -     0B    96K -        9  35.5H  25.32%
> geom{g_up}
> 
> -Alan
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