Is it possible to use different input files (unique files, anyway) of the same size, maybe even on different file systems if available? The creation of these could be scripted along with a dd - don't remove the file immediately after the dd, though. It might be even better if you could issue multiple reads in parallel, though that will be hard to do if it's a really small file.
On Fri, Aug 2, 2013 at 8:58 AM, Steinar H. Gunderson <sgunderson@xxxxxxxxxxx> wrote:
On Fri, Aug 02, 2013 at 09:23:44AM -0400, Mike Snitzer wrote:I tried this, and it still doesn't appear to promote anything at all:
> Yes, it is surprising. Curious to know if the promotions aren't
> happening due to the IO scheduler somehow merging all your random small
> IO. We don't yet have a descrete counter to show the number of
> migrations that were skipped due to sequential_threshold but that is
> something we can add.
>
> But you can effectively disable the sequential_threshold by setting it
> really high, e.g.:
>
> dmsetup message cache 0 sequential_threshold 16384
cache: 0 23440891904 cache 913/8192 0 7021239 0 2049048 0 0 0 0 0 2 migration_threshold 2048 4 random_threshold 8 sequential_threshold 16384
It's only been running for a few minutes, though.
FWIW, earlier I ran it on only one single partition, and then it worked.
So it's not like my kernel is completely broken, at least.
I did, with a 16 kB file (that should certainly be small enough, right?),
> Please write a file that is smaller than your specified
> sequential_threshold, and then read it numerous times via direct IO,
> e.g.:
>
> dd if=<your file> of=/dev/null iflag=direct bs=16K
executing the dd command 10000 times. Still nothing cached.
-- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
