Quoting Jeff Dike <jdike@...>:
> Sorry about the lack of responsiveness.
No problem, I'm glad to read you now.
> I've had such a patch for quite a while. I never stuck it in mainline
> because I couldn't find any common use cases where it made a noticable
> Does your patch help noticably with anything reasonable common?
It did help significantly for me.
On a reasonably new host, using as UBD devices logical volumes built
on top of a FC SAN, building a 10GB ext3 filesystem took something
like 50 seconds before my patch, and something like 3 seconds after
it. (I can check the exact values if you wish.)
Note that this is using CONFIG_UBD_SYNC (or whatever it is called);
without it it gets even faster (but I guess parallel I/O make no
My feeling is that it might improve performance when reads and writes
are performed simultaneously, but I have not made any try.
As for using CONFIG_UBD_SYNC, my feeling is that it's much safer if
the host might crash (or experience power outages, or...): as far as I
understand it, journaled filesystems need to know when data is
actually secured on the discs.
Hope this helps,
Ecole Centrale Paris