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

[Michael S. Tsirkin]

Quoting r. Grant Grundler <iod00d at hp.com>:
> Subject: Re: performance counters in /sys
> 
> On Fri, May 20, 2005 at 10:20:29AM -0600, Ronald G. Minnich wrote:
> > yes, that is the accepted thing nowadays. And, boy, is it SLOW. SLOW,
> > SLOW, SLOW.
> > Open file, read ONE value, close file. Takes a long time. So we've seen 
> > that for a number of values you really can't sample at interesting rates. 
> 
> Exactly. That's Mark's gripe too.
> 
> > Of course, you can speed it up a bit -- keep your files open, right?
> > open once, read, fseek 0, read, ...
> > Except then, if you need to unload the module, well, you can't: you have
> > the /sys files open and the module can't really be unloaded.
> 
> That's good, IMHO.

It will also prevent hotplug from working. So no, I dont think its good.

> Unloading the HCA driver will disable the device.
> On ia64 platforms (and probably PPC too) will lead to hard fail on the
> next MMIO read since the device won't respond to MMIO space accesses.
> 
> "lsof /sys/class/infiniband" would help track down the monitoring tool.

Who would do MMIO reads if the driver is unloaded?

-- 
MST - Michael S. Tsirkin