Arch Linux

hoome

Member

From: Brazil

Registered: 2013-07-18

Posts: 53

Disk IO monopolized by one app

Hi,

I have a desktop and a notebook, by hardware upgrade issues i'm using only my notebook,

On my desktop, i have four hard driver 7200RPM SATA II so i've only notices this problem when using VMWare and i  was thinking that was a VMWare problem, but, now that i'm using more the notebook i've noticed that this problem also affects my notebook, both are Arch Linux.

The notebook hard disk is slowest (it's one WD Blue that operates only at 5400RPM), so, this problem is more grave. When i open a process that consume much hard disk io, like a uncompress a file the Disk Input/Output is monopolized by that app and the system just "hangs" for some seconds, even minutes, until the operation is done.

On desktop i've only noticed that when the VM inside VMWare was using alot of bandwidth, but, on my notebook a simple system upgrade make my music stop until it's finish uncompressing the files, and the music only returns when that process stop to request so much IO. Just an example, both music, web navigation, anything. It's like the disk can't handle multiple access.

On my laptop i don't have VMWare or any heavy applications using the hard drive, only a simple system upgrade is enought to "freeze" the system for some seconds.

The system processor and RAM are ok, i've tested the disk IO usage with iotop, also, it's kinda perceptible that isn't a proc/mem issue.

Last edited by hoome (2013-08-22 17:04:42)

brebs

Member

Registered: 2007-04-03

Posts: 3,742

Re: Disk IO monopolized by one app

You can help by giving hints to your system as to how it should prioritize itself, e.g. the nice command, and especially ionice -c3

Pse

Member

Registered: 2008-03-15

Posts: 415

Re: Disk IO monopolized by one app

Hmm, I haven't experienced what you describe (I'm typing this from a 5400rpm notebook hard-drive). I usually run several VMs, heavy IDEs (Eclipse, IntelliJ) and many Chromium tabs at the same time, and update the system while doing that. Music never skips. I'm running the stock Arch kernel with the default schedulers. Have you modified any settings? Scheduler, sysctls, etc? What kind of hardware do you run? Can you try a Fedora or Ubuntu live-CD to compare?

rufus

Banned

From: san francisco

Registered: 2013-04-20

Posts: 153

Re: Disk IO monopolized by one app

@hoome you say everything is working right with memory and such but didnt mention how much you have nor your cpu...
is this a new problem or ? watch htop for awhile see if anything is being a pig. there are many tweaks one can do to speed up writes
I dont see or hear a specific problem other than maybe needing to upgrade hardware. there are many tweaks posted and in the
wiki for enhancing performance....

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hoome

Member

From: Brazil

Registered: 2013-07-18

Posts: 53

Re: Disk IO monopolized by one app

@rufus The desktop is a AMD Phenom II x6 1090T at 3.2GHz (Six Core) with 8GB of RAM and the notebook is a Intel i3 (dual core with HT) at 2.2GHz with 4GB of RAM, both x86_64. The notebook is at ondemand and plugged on AC Changer when i've tested. On desktop i've tested ondemand and performance modes.

A small detail, like @brebs,i don't use Swap on both desktop and notebook, it may be related, but i've never got the memory full.

the htop shows low usage (5%/10%) of memory/proc on both computers, but heavly IO usage (near 95%/100%).

I will try the tip from @brebs when i get home.

@Pse i've not changed any scheduler settings or compiled a new kernel, is the stock, i've add some apps to run at boot with systemctl, i don't know if it's related but when i got home i paste the list of apps running by systemd at boot.

@Pse i was using Debian Testing (Jessie) on both computers and i didn't have this problem.

Last edited by hoome (2013-08-26 13:38:44)

Pse

Member

Registered: 2008-03-15

Posts: 415

Re: Disk IO monopolized by one app

If Debian testing works OK, then we can probably rule out hardware issues. Could you post the output of 'iotop' both when everything appears to be OK, and when stuttering is occurring?

Edit: extra question: what filesystems are you using?

Last edited by Pse (2013-08-26 18:14:49)

hoome

Member

From: Brazil

Registered: 2013-07-18

Posts: 53

Re: Disk IO monopolized by one app

@Pse I was copying some movies (~200GB) from a Brand New 2TB 7200RPM 64MB Seagate SATA III Hard Drive to another Brand New 2TB 7200RPM 64MB Seagate SATA III Hard Drive on my desktop and the music stops and starts to buffer several times, not only the music, web browsing and general apps are slow (i think that they are trying to add data to the hard drive and getting the same problem as musics).

I managed to take a screenshot of iotop on one of those buffers:

Click to get bigger

@Pse i'm using ext4 with relatime and root reserved of 1%.

ps. those hard drivers are pratically empthy, has less than 10% of use.

Edit: And the genfstab add a option data=ordered on my fstab, what is it? has some relation with the problem? On my debian i jsut use relatime and rw options.

Last edited by hoome (2013-08-31 00:09:17)