Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 25 Feb 2003 11:24:58 -0800 | From | Patrick Mansfield <> | Subject | Re: 2.5.62-mm2 slow file system writes across multiple disks |
| |
On Mon, Feb 24, 2003 at 08:43:21PM -0800, Andrew Morton wrote: > Patrick Mansfield <patmans@us.ibm.com> wrote:
> > I moved to 2.5.62-mm3 [I had to drop back to qlogicisp for my boot disk, > > and run the feral drver as a module in order to boot without hanging], and > > ran write-and-fsync with -f, with and without -o (O_DIRECT).
> Is this using an enormous request queue or really deep TCQ or something? > I always turn TCQ off, stupid noxious thing it is.
Yes - pretty high, the feral driver is defaulting to 63 (comments there say "FIX LATER"). Changing it to 8 gave much improved performance.
I'm on a slightly different kernel, anyway:
10 fsync writes of 200 mb to 10 separate disks, queue depth (TCQ) of 63 gave:
0.05user 37.14system 1:09.39elapsed 53%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (1986major+3228minor)pagefaults 0swaps
10 fsync writes of 200 mb to 10 separate disks, queue depth of 8 gave:
0.05user 38.56system 0:32.71elapsed 118%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (1986major+3228minor)pagefaults 0swaps
The total time dropped by almost half. vmstat numbers were much smoother.
It would be nice if a larger queue depth did not kill performance.
The larger queue depths can be nice for disk arrays with lots of cache and (more) random IO patterns.
-- Patrick Mansfield - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| ![\](/images/icornerr.gif) |