On Tue, Mar 27, 2018 at 12:23:33AM +0200, Jaromír Dole?ek wrote:
> > Independent of how the scaling problem will be handled, I suggest to
> > increase that window to at least MAXPHYS.
>
> I think the file mapping window doesn't need to really be tied to MAXPHYS.
> But values over MAXPHYS will probably currently [*] not give further
> significant speedup for filesystem I/O, unless data is being read from cache.
Yes, that's why MAXPHYS might be a good value.
> Did the experiment work?
UBC_WINSHIFT=17 (i.e. 2*MAXPHYS) works fine, but sure, for KVA limited
platforms you have to be careful. On the other hand, it's a temporary
mapping that only exists while doing I/O. How many concurrent I/O
operations would you expect on a 32bit system?
> [*] I hope to get tls-maxphys integrated for 9.0, by then maybe we need
> to revisit this. It would be also nice to revisit the need to map the
> memory to kernel pmap in order to do the I/O.
I'd also like to get another tuning to 8.0. Bumping RA_WINWIZE_MAX
from 8*MAXPHYS to 16*MAXPHYS helps iSCSI and maybe some nvme devices
too.
Greetings,
--
Michael van Elst
Internet: mlel...@serpens.de
"A potential Snark may lurk in every tree."
