[Bug 131094] Re: Heavy Disk I/O harms desktop responsiveness

[Hendrik van den Boogaard]

Update: running with 'mem=512m' seems to make performance just as bad as
on older/other kernels. Then I recalled some information about native
command queueing (thanks for the hint on your picture Jamie :)) and how
this could trash your disk on some older drive models. I already
disabled it on my fileserver a couple of months/years ago and now tried
the following:

Copy the large files in one window (PATA -> SATA) and do a 'find /'
(SATA drive) in the other window. I found out that the 'find' command is
a *lot* more responsive pushing file names to the screen when I put the
NCQ buffer on 1 item (effectively disabling NCQ). The mouse and cursor
still lock up often for less than a second and performance is still
sluggish but the machine is not completely unusable. While I am typing
this I put the NCQ setting back to 31 as it was on before but now I
cannot even type this complete sentence without seeing it appear on the
screen. As far as I can remember somewhere in the 2.6.1x kernels NCQ was
added together with all the new libata stuff (that's for me when a lot
of trouble started; a bad sector on a disk created kernel-oopses on
another NVidia based computer with a 4TB software Raid5 Array). This
might also explain why I have not seen this problem before as my old
160G drive is PATA and has no NCQ.

I am wondering if anyone else tried this or can verify this against my
experiences.

Another interesting observation: When I 'cat * > /de/null' from the
large files directory on the SATA disk performance is sluggish, tabbing
through windows is slow to unbearably slow. When I do the 'cat * >
/de/null' on the PATA drive there is no sluggishness AT ALL! The swap
was turned off to make sure that alt-tabbing would not load paged-out
data from the SATA disk, but even after turning swap over to the PATA
disk, performance stayed the same when catting on the PATA disk.  Same
for xfs_fsr defragmentation on SATA: slow and sluggish (also, but a bit
less with NCQ off) and on PATA my GUI just remains responsive!

So afterall this really seems to SATA related!

-- 
Heavy Disk I/O harms desktop responsiveness
https://bugs.launchpad.net/bugs/131094
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