linux-kernel - Re: [PATCH v1] PCI / PM: Really allow runtime PM without callback functions

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Date: Wed, 14 Feb 2024 10:06:52 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Raag Jadav <raag.jadav@...el.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	bhelgaas@...gle.com, jarkko.nikula@...ux.intel.com,
	mika.westerberg@...ux.intel.com, stanislaw.gruszka@...ux.intel.com,
	lukas@...ner.de, rafael@...nel.org, ilpo.jarvinen@...ux.intel.com,
	linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
	sashal@...nel.org
Subject: Re: [PATCH v1] PCI / PM: Really allow runtime PM without callback
 functions

On Wed, Feb 14, 2024 at 03:20:35PM +0200, Raag Jadav wrote:
> On Wed, Feb 14, 2024 at 03:01:29PM +0200, Andy Shevchenko wrote:
> > On Wed, Feb 14, 2024 at 12:43:35PM +0200, Raag Jadav wrote:
> > > On Tue, Feb 13, 2024 at 02:06:48PM -0600, Bjorn Helgaas wrote:
> > > > On Mon, Feb 12, 2024 at 12:02:33PM +0530, Raag Jadav wrote:
> > 
> > ...
> > 
> > > > >  0)               |  pm_runtime_work() {
> > > > >  0)               |    rpm_idle() {
> > > > >  0)               |      rpm_check_suspend_allowed() {
> > > > >  0)   1.500 us    |        __dev_pm_qos_resume_latency(); /* = 0x7fffffff */
> > > > >  0)   4.840 us    |      } /* rpm_check_suspend_allowed = 0x0 */
> > > > >  0)   1.550 us    |      __rpm_get_callback(); /* = 0xffffffffb4bc84f0 */
> > > > >  0)   1.800 us    |      pci_pm_runtime_idle(); /* = -38 */
> > > > >  0) + 17.070 us   |    } /* rpm_idle = -38 */
> > > > >  0) + 22.450 us   |  } /* pm_runtime_work = -38 */
> > > > 
> > > > What is this timing information telling me?
> > > 
> > > It's a raw ftrace dump.
> > 
> > (Told ya that people would be surprised with this without seeing how you get
> >  this and what fields mean)
> 
> I can add stat headers in v2 which I think will be more helpful.

That's not what I was asking.  *Why* is the ftrace dump here?  Is the
point that we're calling a function we shouldn't?  That this patch
improves performance?  Without some interpretation of what the dump
shows, it's just noise.

Bjorn