On 6/17/22 14:43, Miklos Szeredi wrote:
On Fri, 17 Jun 2022 at 11:25, Bernd Schubert <bernd.schubert@xxxxxxxxxxx> wrote:
Hi Miklos,
On 6/17/22 09:36, Miklos Szeredi wrote:
On Fri, 17 Jun 2022 at 09:10, Dharmendra Singh <dharamhans87@xxxxxxxxx> wrote:
This patch relaxes the exclusive lock for direct non-extending writes
only. File size extending writes might not need the lock either,
but we are not entirely sure if there is a risk to introduce any
kind of regression. Furthermore, benchmarking with fio does not
show a difference between patch versions that take on file size
extension a) an exclusive lock and b) a shared lock.
I'm okay with this, but ISTR Bernd noted a real-life scenario where
this is not sufficient. Maybe that should be mentioned in the patch
header?
the above comment is actually directly from me.
We didn't check if fio extends the file before the runs, but even if it
would, my current thinking is that before we serialized n-threads, now
we have an alternation of
- "parallel n-1 threads running" + 1 waiting thread
- "blocked n-1 threads" + 1 running
I think if we will come back anyway, if we should continue to see slow
IO with MPIIO. Right now we want to get our patches merged first and
then will create an updated module for RHEL8 (+derivatives) customers.
Our benchmark machines are also running plain RHEL8 kernels - without
back porting the modules first we don' know yet what we will be the
actual impact to things like io500.
Shall we still extend the commit message or are we good to go?
Well, it would be nice to see the real workload on the backported
patch. Not just because it would tell us if this makes sense in the
first place, but also to have additional testing.
I really don't want to backport before it is merged upstream - back
porting first has several issues (like it gets never merged and we need
to maintain for ever, management believes the work is done and doesn't
plan for more time, etc).
What we can do, is to install a recent kernel on one of our systems and
then run single-shared-filed IOR over MPIIO against the patched and
unpatched fuse module. I hope I find the time later on today or latest
on Monday.
Thanks,
Bernd
