SSDs peformance on head/freebsd-10 stable using FIO

[Kashyap Desai]

> -----Original Message-----
> From: Alexander Motin [mailto:mavbsd at gmail.com] On Behalf Of Alexander
> Motin
> Sent: Monday, July 14, 2014 2:54 PM
> To: Kashyap Desai
> Cc: FreeBSD-scsi
> Subject: Re: SSDs peformance on head/freebsd-10 stable using FIO
>
> On 14.07.2014 11:36, Kashyap Desai wrote:
> > From: Alexander Motin [mailto:mavbsd at gmail.com] On Behalf Of
> Alexander
> >> First thing I noticed in this profile output is bunch of TLB shutdowns.
> >> You can not reach reasonable performance from user-level without
> >> having HBA support unmapped I/O. Both mps and mpr drivers support it,
> >> but for some reason still not mrsas. Even at non-peak I/O rates on
> >> multi-core system TLB shutdowns in such case can eat additional 30%
> >> of CPU time.
> >
> > Thanks.! For this part, I can try In mrsas. Can you help me to
> > understand what you mean by unmapped I/O ?
>
> That is a capability to work with data not mapped into the kernel virtual
> address space, i.e. to work with physical addresses instead of virtual.
> Main
> prerequisite to support that is that driver should not try to access the
> transferred data (because it can't do it for addresses not mapped to KVA).
> If
> that is true, then usually only minor modification is needed to teach the
> driver to receive physical addresses from CAM.
>
> Looking on mps driver as example you may see PIM_UNMAPPED flag
> reporting unmapped I/O support to CAM, and bus_dmamap_load_ccb()
> helper function transparently doing all the physical address handling
> magic.

Thanks Motin.. I got the what is an issue here about UNMAPPED IO.
Konstantin Belousov posted below performance result and there was also a
changes in <mfi> to use Unmapped IO.

https://kib.kiev.ua/kib/pgsql_perf.pdf

I will work on this (will refer mpt driver ) and get back to FreeBSD
Developers to seek any help..

` Kashyap


>
> --
> Alexander Motin