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** Changed in: linux (Ubuntu)
Status: Incomplete => Won't Fix
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https://bugs.launchpad.net/bugs/343371
Title:
Very poor desktop response (high latency) during I/O-load with
SATA+NCQ
Status in linux package in Ubuntu:
Won't Fix
Bug description:
Binary package hint: linux-image-2.6.27-13-generic
I run Ubuntu on a moderately powerful quad-core x86-64 system and the
desktop response is basically crippled whenever something is reading
or writing large files as fast as it can (at normal priority).
As an example scenario:
1) Do: $ cat /path/to/LARGE_FILE > /dev/null
This will start a process reading a large file as fast as it can.
2) Everything else gets completely unusable because of the I/O latency.
Opening a new Firefox tab takes seconds,
loading a web page takes ages, reading email with Evolution is extremely
slow, etc. Basically anything that needs
to read or write something to disk, other than the cat process, is slowed
down to a crawl (I/O-starved). Forget about starting up new programs, they will
only appear after the process started in 1) has finished completely with
dumping the entire file to /dev/null. As an example here, I launched 'gedit' as
soon as I had started 1), and it appeared only after cat exited.
3) As soon as the cat-process is finished, everything gets back to
normal and system is fine and snappy again.
4) The throughput itself is good, but the problem is that it
completely starves the rest of the system I/O-wise, using only Ubuntu
default settings.
It shouldn't be like this for a deskop-oriented distro on relatively
powerful hardware (quad-core CPU, 64bit, 8GM RAM).
Disabling NCQ, by doing:
$ echo 1 > /sys/block/sda/device/queue_depth #(as per
http://linux-ata.org/faq.html)
improves the situation quite a bit, but it is still painful, and not
as fair as one would like when using "Completely Fair Queuing"
I/O-scheduler under read-load. Write load is also painful, i.e. when
copying large files from a different drive to the main SATA drive, or
copy from drive to itself. Except for the issue at hand, there are no
problems with hard drive performance or system stability in general.
System summary:
Ubuntu Intrepid x86-64 (using kernel 2.6.27-13)
Disk mount options at defaults, I/O-scheduler is default CFQ.
The main hard drive holds both root partition and /home-partition. All
relevant
file systems are EXT3 with Ubuntu default mount options (ordered, relatime).
NCQ is enabled for this particular drive (libata reports depth 31/32 at boot).
Hardware:
ASUS P5E WS Pro, Intel X38 Express / Intel ICH9R
Intel(R) Core(TM)2 Quad CPU Q9300 @ 2.50GHz
8 GB RAM
Main SATA controller: Intel Corporation 82801IR/IO/IH (ICH9R/DO/DH) 6 port
SATA AHCI Controller (rev 02)
Main hard drive: Western Digial WD5000AACS-00ZUB0, SATA NCQ enabled.
I will attach:
1) Output of command 'lspci -vv', run as root
2) Kernel log from boot
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