Re: Bad fs performance, IO freezes

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

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On 2015-10-27 09:00, Henk Slager wrote:
> I don't have a lot experience with autodefrag, but as indicated by
> Austin, expect a lot of full rewrites of files that are relatively
> slowly filled up by a torrent client, starting with a sparse file. So
> 1st advice would be to remove this option and run it as crontask at
> particular times.
>
> What SATA-USB bridge is between the harddisk and the PC motherboard ?
I hadn't thought of this, but the specific adapter being used for the 
disk can have a lot of impact on how it preforms.  I've personally had 
lots of issues with JMicron chipsets (ranging from latency issues like 
what you are seeing to sever data corruption), but have found that 
ASMedia ones tend to be pretty much rock solid reliable and have good 
performance (although I think they only do USB 3.0 adapters).
> Also what USB host chipset is on the PC motherboard ?
If it's a Intel motherboard, the USB 2.0 ports are probably routed 
through on-board hubs to the ports provided by whatever Intel calls 
their equivalent of the south bridge these days, and the USB 3.0 ports 
are probably a mix of Intel and ASMedia XHCI controllers (ASMedia was 
one of the first companies to do an inexpensive standalone XHCI chip, so 
they're relatively popular for extra USB 3.0 ports).  FWIW, the first 
generation of Intel XHCI chips had some issues with older Linux kernels, 
although IIRC those issues were along the lines of a port just 
disappearing after disconnecting whatever was connected to it.
> Why don't you run 64-bit Ubuntu on this core i7 ?
64 versus 32 bit shouldn't cause anything like this to happen (although, 
if it can be proven that it does, then that is a serious bug that needs 
to be fixed).  That said, unless you have some desperate need to be 
running 32-bit only, you should seriously look into updating to a 64-bit 
version, your whole system should run faster, and Ubuntu has really good 
32-bit compatibility in the 64-bit version (which is part of why it's 
popular as a support target for third party software like Steam).
>
>
> On Tue, Oct 27, 2015 at 12:44 PM, Austin S Hemmelgarn
> <ahferroin7@gmail.com> wrote:
>> On 2015-10-26 22:00, cheater00 . wrote:
>>>
>>> Hello,
>>> currently my computer freezes every several seconds for half a second
>>> or so. Using it feels like I'm playing musical chairs with the kernel.
>>> I have just one download happening on utorrent right now - this is
>>> what the graph looks like:
>>> http://i.imgur.com/LqhMtrJ.png
>>> and every time a new spike happens, a freeze happens just before
>>> that... that's the only time those freezes happen, too.
>>>
>> Do you have the 'autodefrag' mount option enabled?  If it is turned on, then
>> that may be the problem.  Most bittorrent clients pre-allocate the space for
>> a download, then write each block directly into the location it's supposed
>> to be in the resultant download, which means depending on how it's
>> pre-allocating the space, that you end up with a large number of randomly
>> ordered writes into a single file, which in turn will trigger the autodefrag
>> code, which can cause latency spikes when you're also hitting the disk at
>> the same time.



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