I/O Blocking

Hi,

Both the RAID (Promise SuperTrak 6000) or the USB subsystems really drive the system load up. I'm using a AMD 3200+ system that is only a few months old with the 2.4.25 kernel. When the I/O systems are blocking the system is very unresponsive. Some times samba will timeout, or I'll wait several seconds for commands like df, top, w and so on.

I am wondering if I were to use a dual CPU system, would this solve my I/O blocking problem? Would one CPU tend to the I/O subsystem and the second would deal with other system requests I (samba, DB, LDAP, ...)?

What is the CPU load like? Are you at 100%? If so a second CPU may help. If you are blocked on i/o it should not use much CPU, so my guess is your CPU load is very low, and a second CPU won't do much. How much RAM do you have? Are you swapping?

Guy

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Jason C. Leach
Sent: Thursday, July 22, 2004 12:29 PM
To: [email protected]
Subject: I/O Blocking

Hi,

Both the RAID (Promise SuperTrak 6000) or the USB subsystems really drive the system load up. I'm using a AMD 3200+ system that is only a few months old with the 2.4.25 kernel. When the I/O systems are blocking the system is very unresponsive. Some times samba will timeout, or I'll wait several seconds for commands like df, top, w and so on.

I am wondering if I were to use a dual CPU system, would this solve my I/O blocking problem? Would one CPU tend to the I/O subsystem and the second would deal with other system requests I (samba, DB, LDAP, ...)? -
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Guy:

CPU load is very low (95-96% idle), load avg is 2. The system has 512MB RAM, some free and only a few megs swapped out. If I was really working the RAID card I would get load avgs more like 2.5-3. Right now just light USB and system usage and I am at 2.

I though if one CPU was tied up with the process that is blocking (using the RAID card), then the second would be free to deal with user requests. Or am I misunderstanding SMP and blocking I/O?

J.

If your 1 CPU is 95% idle, it can do other "user requests". But not if the other "user requests" require disk I/O, they will also block regardless of which CPU they are using. I think there is a performance problem with your disks. But just a guess.

Guy

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Jason C. Leach
Sent: Thursday, July 22, 2004 2:10 PM
To: Guy
Cc: [email protected]
Subject: Re: I/O Blocking

Guy:

CPU load is very low (95-96% idle), load avg is 2. The system has 512MB RAM, some free and only a few megs swapped out. If I was really working the RAID card I would get load avgs more like 2.5-3. Right now just light USB and system usage and I am at 2.

I though if one CPU was tied up with the process that is blocking (using the RAID card), then the second would be free to deal with user requests. Or am I misunderstanding SMP and blocking I/O?

J.

-
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Jason,

There is a technical answer to your question which I cannot properly relate to you. The practical answer is yes, an SMP system will generally perform better under heavy interrupt conditions and would probably help with the situation you are having.

That said, the problem you are having is not lack of CPU performance. I don't know what it is but you need to look into it before throwing another mega-cpu at it. You might have too many I/O devices sharing the same IRQ, it could be something weird like a haywire parallel port device. Take a careful look at how your equipment is set up and do some experiments turning things off and on, etc. You can probably get to the bottom of it without upgrading anything.

-Kanoa

HMMM I seemed to have lost the 1st of the thread, 2 cents worth .. what ya pay for ...

I might be supect of the m/b IDE channels (personally had lots of failures) - SMART drives that are not configured as SMART (sorry, I always use Intel, AMD...?) enableing in bios and kernel or mod might give clues. I, also, think that there must be an IRQ conflict, IRQ unanswered, or same ilk.

You could test by swapping drives, swapping m/b's. What sizes are your disks? What RAM do you use,, I do have a plethora of hwde I could loan.

b-