Re: huge improvement with per-device dirty throttling

[Al Boldi <a1426z@gawab.com>]

Jeffrey W. Baker wrote:
> I tested 2.6.23-rc2-mm + Peter's per-BDI v9 patches, versus 2.6.20 as
> shipped in Ubuntu 7.04.  I realize there is a large delta between these
> two kernels.
>
> I load the system with du -hs /bigtree, where bigtree has millions of
> files, and dd if=/dev/zero of=bigfile bs=1048576.  I test how long it
> takes to ls /*, how long it takes to launch gnome-terminal, and how long
> it takes to launch firefox.
>
> 2.6.23-rc2-mm-bdi is better than 2.6.20 by a factor between 50x and
> 100x.
:
:
> Yes, you read that correctly.  In the presence of a sustained writer and
> a competing reader, it takes more than 30 minutes to start firefox.
>
> 4.
>
> du -hs /bigtree
>
> Under 2.6.20, lstat64 has a mean latency of 75ms in the presence of a
> sustained writer.  Under 2.6.23-rc2-mm+bdi, the mean latency of lstat64
> is only 5ms (15x improvement).  The worst case latency I observed was
> more than 2.9 seconds for a single lstat64 call.
:
:
> In other words, under 2.6.20, only writing processes make progress.
> Readers never make progress.
>
> 5.
>
> dd writeout speed
>
> 2.6.20: 36.3MB/s, 35.3MB/s, 33.9MB/s
> 2.6.23: 20.9MB/s, 22.2MB/s
>
> 2.6.23 is slower when writing out, because other processes make progress
>
> My system is a Core 2 Duo, 2GB, single SATA disk.

Many thanks for your detailed analysis.

Which io-scheduler did you use, and what numbers do you get with other 
io-schedulers?


Thanks!

--
Al