async buffer flushing reported slowdown (could be a driver issue?)

Andrea Arcangeli
2002-01-17T14:17:31Z

On Wed, Jan 16, 2002 at 04:29:54PM -0500, Adam Kropelin wrote:
> Andrea Arcangeli wrote:
> <snip>
> >I don't have a single bugreport about the current 2.4.18pre2aa2 VM (except
> >perhaps the bdflush wakeup that seems to be a little too late and that deals to
> >lower numbers with slow write load etc.., fixable with bdflush tuning).
>
> I don't know if this is a reference to the issue I reported under the "Writeout in
> recent kernels..." thread or not. If not, my apologies for clogging up this new
> "discussion".

yes, I was thinking about you report.

>
> As reported[0] in the above-mentioned thread, the bdflush tuning parameters
> you suggested made no difference in my test case other than slightly adjusting
> the temporal relationship between writeout and file transfer. -aa still performs
> slightly worse than both 2.4.17 stock and -rmap. 2.4.13-ac7 currently beats
> all competitors.

Then can you verify the bandwith you get out of the network card is the
same across 2.4.13-ac7 and all the other kernels you are trying. Also
please check with an hdparm -t the speed you get out of IDE is the same.
This sounds like some driver changed (note that -ac is used to queue
lots of driver updates) and that made the difference. Otherwise if we
wakeup bdflush early enough I don't see why it takes more time.

Andrea