07-03-2012
Quote:
Originally Posted by
nytty
Alright, I get your point. I though that using /dev/sdb1 moves to position 0
AFAIK hdparm only gives you the speed of the disk and not the time of reading a given amount of data.
Do a little math. x megabytes per second is 1/x seconds per megabyte.
Quote:
So far with my tests I find that reading 16kb takes about the same time as reading 512b.
Disks do read-ahead for you. Disks transfer to the host in larger bundles than 512 bytes anyway. Disks even do their own
caching which the OS has no control over, which is going to throw off all your results supremely.
Too bad there isn't a tool which can tell you more about what your disk's doing, test uncached reads, or even configure hardware read-ahead to your preference... something like hdparm...
Quote:
I need this information to set the optimal page size of my system (oracle and mysql suggest these sizes)
Tell me exactly what they're asking you. I suspect you've gotten it a bit mixed up.
Quote:
Can you elaborate on why dropping the caches is a bad idea?
Because it's not realistic. Your system needs cache to work. Disk speeds are going to be awful without it.
Quote:
How about this sudo procedure:
- drop_caches
- flush disk-cache with hdparm
- make sure dd is in memory
- position the read head randomly on disk
- with DD: read X amount of bytes from the beginning of my file (this is timed)
Same problem as the exact same thing you did before. YOu're running huge programs to do tiny things and your results are going to be meaningless.
Last edited by Corona688; 07-03-2012 at 04:51 PM..
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LEARN ABOUT DEBIAN
smfplay
SMFPLAY(1) BSD General Commands Manual SMFPLAY(1)
NAME
smfplay -- play a standard MIDI file
SYNOPSIS
smfplay [-mxy] [-g measure] [-d devname] [-i devname] midifile
DESCRIPTION
The smfplay utility plays a MIDI file. While playing, it can route events from one midi(4) device to another. To stop performance, send an
interrupt signal to smfplay (for instance by pressing control ^C on the terminal). The options are as follows:
-m Use metronome. The metronome will follow tempo changes and time signature changes in the midi file.
-x Synchronise to an external midi(4) device. If the -i flag is used then playback will be synchronised to the input device else it
will be synchronised to the default device.
-y Send midi timing information to the default device. Useful if the output device is a slave MIDI sequencer.
-g measure Start playback at the given measure number.
-d filename Default midi(4) device on which to play the midi file. If not specified, the content of the MIDIDEV environment variable will be
used instead.
-i filename Alternate input midi(4) device. Voice events (notes, controllers, etc) received on the input device will be sent as-is to the
default device. Without this flag, the default device will be used for input.
The smfplay utility is an interface to midish(1). If more specific features are needed, the user may consider using midish(1).
EXAMPLES
The following will play mysong.mid on device /dev/rmidi4 and will use metronome.
$ smfplay -m -d /dev/rmidi4 mysong.mid
SEE ALSO
smfrec(1), midish(1), midiplay(1), midi(4)
BSD
August 22, 2005 BSD