Single-threaded bottleneck in geli

[Paweł Jakub Dawidek]

Direct dispatch would be great for geli, especially that geli can use own (multiple) threads when necessary (eg. using crypto cards). With AES-NI you could go straight to the disk.

-- 
Paweł Jakub Dawidek



> On Jul 3, 2020, at 13:22, Alan Somers <asomers at freebsd.org> wrote:
> 
> I don't.  What I meant was that a single thread (geom) is limiting the
> performance of the system overall.  I'm certain, based on top, gstat, and
> zpool iostat, that geom is the limiting factor on this system.
> -Alan
> 
>> On Fri, Jul 3, 2020 at 2:18 PM Paweł Jakub Dawidek <pawel at dawidek.net>
>> wrote:
>> 
>> 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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>> 
>> 
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