[SDBUG] interrupts in top broken with SMP kernel

[Bill Stouder-Studenmund]

On Mon, Apr 09, 2007 at 12:02:00PM -0700, Michael J McCafferty wrote:
> Mike,
>         Thanks that is very interesting info about adding multiple PCI 
>         cards.

You didn't say what OS you're doing this on.

>         My problem is that vmstat and top do *not* show the CPU % 
> used by interrupts with the mp kernel, but *do* when the uniproc 
> kernel is used. This is important to me because my testing is only 
> able to generate so many packets per second and bandwidth (therefore 
> interrupts per second), which ends up being under 100% cpu time on 
> the system, so I can't just see what the max the system can handle 
> is. My goal is to determine the % cpu used by the same test scenario 
> and determine which of 3 systems runs a the lowest peak cpu 
> utilization in interrupts. Interrupt handling is what the CPU spends 
> the most time doing during the real work that these systems will do 
> after the test.
>         The problem is that the same software behaves differently 
> with the mp kernel and the uniproc kernel. I was counting on the 
> system telling me the % of maximum interrupt time. For me, the 
> interrupts per second is worthless without knowing how many 
> interrupts per second is the maximum.
>         Part of my goal is to determine if a Core2Duo 6300 
> (2x1.86GHz cores) system will have a higher capacity than a firewall 
> than a P4 3.0GHz. These are also compared to a Celeron 3.3GHz. All of 
> these are candidates to replace the existing Celeron 2.8GHz. The 
> interesting thing is that the existing production system shows 
> significantly higher interrupt time than the tests imply it should... 
> when handling real life traffic. The most obvious difference is that 
> it's handling hundreds of hosts instead of just the two test hosts.
>         I performed this test on all of the systems and found that 
> difference was not as great as one would expect (see below). Then, I 
> realized that I had forgotten to use the mp kernel when testing the 
> Core2 Duo system. The question in my head that I really need to 
> actually *know* the answer to, not guess, surmise, or calculate based 
> on conjecture, is: is the 2 cores better than 1 in this specific 
> application and using the mp kernel.
> 
>         Your thoughts are appreciated.

Take care,

Bill
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 186 bytes
Desc: not available
Url : http://lists.sdbug.org/pipermail/sdbug/attachments/20070409/08528716/attachment.bin