[Bug 192353] Re: 100% CPU usage during disk I/O with SATA

[TheFluffyOne]

I managed to dig out a PATA drive to repeat the above tests on the same
machine. Interestingly, this also wipes out 100% CPU, which I must admit
I wasn't expecting!

$ dd if=/dev/zero of=testfile

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 1  0  34788   5308    560 305108    0    0     1 27740  314  394  2 95  0  3
 1  0  34788   5336    596 305076    0    0    30 30470  311  413  3 93  0  4
 1  0  34788   5824    520 304720    0    0     1 23742  345  453  2 93  0  5
 1  0  34788   5400    540 305212    0    0     5 30498  309  369  7 89  0  4

$ cp testfile anotherfile

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 2  0  34788   5980   1784 302360    0    0 13070 13304  328  476  0 33  0 67
 0  1  34788   5240   1828 303584    0    0 12607 14122  319  456  1 34  0 65
 1  0  34788   5136   1912 304420    0    0 12788 12462  326  462  1 31  0 68
 0  1  34788   5440   1032 305172    0    0 12644 13292  325  453  1 32  0 67

PATA controller as listed by lspci:

00:06.0 IDE interface: nVidia Corporation MCP61 IDE (rev a2)

hdparm information for the PATA drive:

/dev/hda:
 multcount     =  0 (off)
 IO_support    =  1 (32-bit)
 unmaskirq     =  1 (on)
 using_dma     =  1 (on)
 keepsettings  =  0 (off)
 readonly      =  0 (off)
 readahead     = 256 (on)
 geometry      = 36481/255/63, sectors = 586072368, start = 0

Also did some basic comparison between the Windows XP install on the
machine against the Kubuntu install. Used 3 CD images of around 700MB
each, total of 2.1GB as one copy operation:

Windows XP SP2, NTFS, SATA: 1m17s @ ~20% CPU
Kubuntu Linux, EXT3, SATA: 2m40s @ 100% CPU
Kubuntu Linux, EXT3, PATA: 2m57s @ 100% CPU

That makes Windows XP *twice* as fast with only *one fifth* of the CPU
usage!

I ran a further basic test on another machine I have running 64-bit
Kubuntu and this appears to have pretty much the same issue. I'm not
going to include the full spec of this at present as this report is
already a bit spec-heavy; suffice to say it's an Athlon 64 X2 box with
an nVidia chipset (SATA controller is CK804) using sata_nv. OS is
Kubuntu Gutsy 64-bit.

There's something very wrong here. I haven't seen performance like this
since the days when DMA wasn't enabled by default!

** Summary changed:

- 100% CPU usage during disk I/O with SATA
+ 100% CPU usage during disk I/O with SATA/PATA

-- 
100% CPU usage during disk I/O with SATA/PATA
https://bugs.launchpad.net/bugs/192353
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