[openib-general] Re: Re: performance counters in /sys

[Michael S. Tsirkin]

Quoting r. Mark Seger <Mark.Seger at hp.com>:
> Subject: Re: Re: performance counters in /sys
> 
> Since I was the one who originally created this topic I'd like to 
> restate what I said that got this all started.  I'm trying to do 
> relatively lightweight monitoring of lots of system performance counters 
> (on the order of 100-200 or more) across a number of subsystems using 
> standard interfaces.  While I don't feel the need to be able to take 
> 10Ks of samples/sec I would like to at least run efficiently at 1-10/sec 
> range.  I also want to avoid writing custom kernel code and/or talking 
> directly to hardware.
> 
> As I said in my base note I'm currently reading from /proc while some 
> sets of counters are better organized than others, I can still access 
> them relatively efficiently.  While I could certainly "get by" reading 
> one variable per file, I do worry about  the overhead as the sampling 
> frequency goes down.  This will also be a problem as the number of 
> counters and devices grow.  The suggestion about using perfquery would 
> certainly work, but I'd also be concerned about the overhead in running 
> it at smaller sampling intervals.
> 
> I certainly understand the desire to move to sysfs and that 
> /usr/src/linux/Documentation/filesystems/sysfs.txt states that "Mixing 
> types, expressing multiple lines of data, and doing fancy formatting of 
> data is heavily frowned upon. Doing these things may get you publically 
> humiliated and your code rewritten without notice."  However, I don't 
> read this to mean you must only have one data item per file.  For 
> example, I took a look at /sys/block/hda/stat because one of the types 
> of data I collect is disk stats and I was wondering how sysfs dealt with 
> them.  Sure enough, they're all in one file per disk as shown below:
> 
> dl380-2: cat /sys/block/hda/stat
>       0        0        0        0        0        0        0        
> 0        0        0        0
> 
> Also note some of these count bytes, some sectors and other jiffies, so 
> even the units need not be identical.
> 
> -mark

So, what about an actual benchmark for the two approaches that were proposed
(perfquery / sysfs)?


-- 
MST - Michael S. Tsirkin