DragonFly kernel List (threaded) for 2009-08
Re: HAMMER problems with ciss
:Hm, Matt didn't you completely disable SYNCHRONIZE CACHE in 2.3?
:I thought you did! May this results in performance degradation.
:Just my 5 cents :)
No, SYNCHRONIZE CACHE was only disabled for USB attachments in
2.3 (because most USB devices don't handle it). It is enabled
in all other cases.
I did find another problem which might be related. It turns out
our bioqdisksort() was still starving requests. HAMMER is particularly
vulnerable to this because it tends to lay out huge swaths of meta
data before (or after) bulk data. UFS orders the two types of data
too, but on a much smaller cluster-by-cluster basis.
So with HAMMER large pipelined sequential writes can seriously
starve other BIOs, sometimes for many seconds. In anycase, I just
fixed it in head. It might or might not be related to that particular
benchmark. I had already done a similar fix in the NATA driver but
now with AHCI and SILI, which use CAM, I also had to fix the generic
bioqdisksort() as well.
Anything that fsync()'s is going to be nasty in HAMMER no matter what.