Re: [PATCH] PM: add statistics sysfs file for suspend to ram

[Pavel Machek <pavel@ucw.cz>]

On Tue 2011-08-09 00:09:42, Rafael J. Wysocki wrote:
> On Monday, August 08, 2011, Pavel Machek wrote:
> > Hi!
> > 
> > > > > > > Thanks for the nice pointer. I checked dynamic debug. It's really a good debug tool.
> > > > > > > With the dynamic debug:
> > > > > > > 1) user need write a user space parser to process the syslog output;
> > > > > > > 2) Our testing scenario is we leave the mobile for at least hours. Then, check its status.
> > > > > > > No serial console available during the testing. One is because console would be suspended,
> > > > > > > and the other is serial console connecting with spi or HSU devices would consume power. These
> > > > > > > devices are powered off at suspend-2-ram.
> > ...
> > > Not in the case described by Yanmin.
> > 
> > Really? I see the description above.
> > 
> > Yes, they'd need to set up syslog to only log >= KERN_ERR, then parse
> > the (small) results. Even hours worth of suspends should not cause
> > _that_ many errors.
> > 
> > Serial console is irrelevant. You need live machine to dump dmesg, but
> > again, you need live machine to access debugfs, too.
> 
> This sounds like substantial overhead to collect statistics that we can
> collect at a much lower cost in the kernel.

That's always the case, right? Everyone wants different subsets of
syslog, and doing selection in kernel is always lowest overhead.

> The patch isn't very intrusive and rather straightforward.

No, it is not _too_ bad; but

1) the code stays there when not debugging

2) different users want different syslog subsets. Putting all the
"interesting" subsets into /sys/debug/my_syslog_subset just does not
seem like a way to go.

(If anything simpler could be done to help debugging, like generating
udev event on each failed suspend, so that can trigger their
processing, I guess that would be acceptable.)

									Pavel

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