On 2016-02-14 19:20, Otto Moerbeek wrote:
On Sun, Feb 14, 2016 at 06:56:16AM -0500, Donald Allen wrote:
On Sun, Feb 14, 2016 at 1:43 AM, Tinker <ti...@openmailbox.org> wrote:
> Did two tests, one with async and one with softdep, on amd64, 5.9-CURRENT,
> UFS.
>
> (Checked "dd"'s sources and there is no fsync() anywhere in there.
>
> The bufcache setting was 90, 3GB free RAM, pushed 2GB of data using "dd"
> to disk.
>
Based on knowledge of Unices from long ago (not on direct knowledge of
OpenBSD internals), I believe 'dd' uses raw I/O, which bypasses the
buffer
cache.
Those who know the details better than I should comment and correct me
if
I'm wrong, but if I'm right, your test doesn't prove anything about
file-system write caching because your writes didn't go through the
file-system.
Depends where you are writing to: a file or a device?
-Otto
I wrote to a file, as I pointed out it was on UFS which was mounted
either softdep or async.
And, this is where essentially no write caching was experienced, making
me understand that OpenBSD essentially not does write caching (and the
"buffer cache" technically is a read cache).
