Skip to main content

PATA really, really sucks

Trying to figure out why sometimes disk access on my test machine takes way, way too long -- 1000+ ms -- I wrote some test code. My threads ran a function that looks like this: 

write = []
def writer():
    while True:
        start = time.time()
        f = tempfile.TemporaryFile()
        f.write('a' * 4000)
        end = time.time()
        write.append(end - start)

Compare the times for max(write) on a machine with a SATA disk and on one with parallel ATA, where the given number of threads are run for a 10 second period: 

threads         pata    sata
1               6ms      6ms
2               400ms   11ms   
4               1300ms  24ms

Ouch.

I admit I'm not a hardware nerd. Quite possibly I'm missing something, because even PATA shouldn't be THAT bad. Right? hdparm -i says for the PATA disk: 

/dev/hda:

 Model=ST380011A, FwRev=8.01, SerialNo=4JV59KZT
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs RotSpdTol>.5% }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=unknown, BuffSize=2048kB, MaxMultSect=16, MultSect=off
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=156301488
 IORDY=on/off, tPIO={min:240,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4
 DMA modes:  mdma0 mdma1 mdma2
 UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5
 AdvancedPM=no WriteCache=enabled
 Drive conforms to: ATA/ATAPI-6 T13 1410D revision 2:

 * signifies the current active mode

Comments

Anonymous said…
Your SATA interface probably supports something like native command queueing?

This isn't supported by PATA but a lot of the newer SATA chipsets support this, so a hard disk receives all blocks and can it reorder like it preferes.
4:33 AM
Anonymous said…
When you send command to a ide unit, ide is supposed to wait until the drive answers, ie: you've to wait until the command is answered before submitting the second command, which may be what you're seeing (of course things get _much_ worse when you've two hard drives in the same ide cable...)


Anyway - what you're measuring is maxmum latency. What about throughput?
6:33 AM
Unknown said…
This comment has been removed by the author.
11:37 PM
Post a Comment

Popular posts from this blog

Python at Mozy.com

At my day job, I write code for a company called Berkeley Data Systems. (They found me through this blog, actually. It's been a good place to work.) Our first product is free online backup at mozy.com . Our second beta release was yesterday; the obvious problems have been fixed, so I feel reasonably good about blogging about it. Our back end, which is the most algorithmically complex part -- as opposed to fighting-Microsoft-APIs complex, as we have to in our desktop client -- is 90% in python with one C extension for speed. We (well, they, since I wasn't at the company at that point) initially chose Python for speed of development, and it's definitely fulfilled that expectation. (It's also lived up to its reputation for readability, in that the Python code has had 3 different developers -- in serial -- with very quick ramp-ups in each case. Python's succinctness and and one-obvious-way-to-do-it philosophy played a big part in this.) If you try it out, pleas...
9 comments
Read more

A week of Windows Subsystem for Linux

I first experimented with WSL2 as a daily development environment two years ago. Things were still pretty rough around the edges, especially with JetBrains' IDEs, and I ended up buying a dedicated Linux workstation so I wouldn't have to deal with the pain.  Unfortunately, the Linux box developed a heat management problem, and simultaneously I found myself needing a beefier GPU than it had for working on multi-vector encoding , so I decided to give WSL2 another try. Here's some of the highlights and lowlights. TLDR, it's working well enough that I'm probably going to continue using it as my primary development machine going forward. The Good NVIDIA CUDA drivers just work. I was blown away that I ran conda install cuda -c nvidia and it worked the first try. No farting around with Linux kernel header versions or arcane errors from nvidia-smi. It just worked, including with PyTorch. JetBrains products work a lot better now in remote development mod...
Post a Comment
Read more

A review of 6 Python IDEs

(March 2006: you may also be interested the updated review I did for PyCon -- http://spyced.blogspot.com/2006/02/pycon-python-ide-review.html .) For September's meeting, the Utah Python User Group hosted an IDE shootout. 5 presenters reviewed 6 IDEs: PyDev 0.9.8.1 Eric3 3.7.1 Boa Constructor 0.4.4 BlackAdder 1.1 Komodo 3.1 Wing IDE 2.0.3 (The windows version was tested for all but Eric3, which was tested on Linux. Eric3 is based on Qt, which basically means you can't run it on Windows unless you've shelled out $$$ for a commerical Qt license, since there is no GPL version of Qt for Windows. Yes, there's Qt Free , but that's not exactly production-ready software.) Perhaps the most notable IDEs not included are SPE and DrPython. Alas, nobody had time to review these, but if you're looking for a free IDE perhaps you should include these in your search, because PyDev was the only one of the 3 free ones that we'd consider using. And if you aren...
36 comments
Read more