hdparm -t yields incorrect timings when Intel hyperthreading is enabled
Running Wheezy 7.4, kernel 3.2.0-4-686-pae, also on Debian backports
kernel 3.12-0.bpo.1-686-pae
sudo hdparm -t /dev/sda
/dev/sda: # Hyperthreading enabled in bios
Timing buffered disk reads: 36 MB in 3.06 seconds = 11.77 MB/sec
# Apparently not correct
/dev/sda: # Hyperthreading disabled in bios
Timing buffered disk reads: 444 MB in 3.01 seconds = 147.38 MB/sec #
Expected for WD10EZRX
I've formed the habit of using hdparm to vet basic disk operation when I
build a new system. Recently I built a system based upon the Intel Atom
dn2800mt motherboard. When I went to vet disk bandwidth, I obtained
unexpectedly slow readings from hdparm. I found that if I disable
hyperthreading in the bios, bandwidth readings are as expected. I
believe the numbers reported by hdparm are incorrect when hyperthreading
is enabled. There is no other evidence of disk bandwidth problems, and
with hyperthreading enabled the system boots slightly faster to ethernet
up, 11.92s, vs 12.45s:
[ 12.454118] e1000e: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow
Control: Rx/Tx # hyperthreading disabled in bios
Has anyone else experienced this problem? I'm wondering if it is general
to hyperthreading or specific to my particular atom based machine.
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