There may also be more memory coping involved instead of just passing pointers around as well, but I'm not 100% sure.
----------------
Robert LeBlanc
PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1
Robert LeBlanc
PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1
On Mon, Jun 24, 2019 at 10:28 AM Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote:
On Mon, 2019-06-24 at 15:51 +0200, Hervé Ballans wrote:
> Hi everyone,
>
> We successfully use Ceph here for several years now, and since recently,
> CephFS.
>
> From the same CephFS server, I notice a big difference between a fuse
> mount and a kernel mount (10 times faster for kernel mount). It makes
> sense to me (an additional fuse library versus a direct access to a
> device...), but recently, one of our users asked me to explain him in
> more detail the reason for this big difference...Hum...
>
> I then realized that I didn't really know how to explain the reasons to
> him !!
>
> As well, does anyone have a more detailed explanation in a few words or
> know a good web resource on this subject (I guess it's not specific to
> Ceph but it's generic to all filesystems ?..)
>
> Thanks in advance,
> Hervé
>
A lot of it is the context switching.
Every time you make a system call (or other activity) that accesses a
FUSE mount, it has to dispatch that request to the fuse device, the
userland ceph-fuse daemon then has to wake up and do its thing (at least
once) and then send the result back down to the kernel which then wakes
up the original task so it can get the result.
FUSE is a wonderful thing, but it's not really built for speed.
--
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
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