linux-kernel - Re: `pci_apply_final_quirks()` taking half a second

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Message-ID: <1491670819.6021.33.camel@infradead.org>
Date:   Sat, 08 Apr 2017 19:00:19 +0200
From:   David Woodhouse <dwmw2@...radead.org>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: `pci_apply_final_quirks()` taking half a second

On Sat, 2017-04-08 at 10:41 -0500, Bjorn Helgaas wrote:
> 
> > Measuring where time is spent during boot with `systemd-bootchart`
> > on an Asus A780FullHD, it turns out that half a second is spent in
> > `pci_apply_final_quirks()`.
> 
> I agree, that seems like a crazy amount of time.
> 
> Can you figure out how to turn on pr_debug() (via the dynamic debug
> mess or whatever) and boot with "initcall_debug"?  That should tell us
> how long each quirk took.

It could well be spending a fair amount of time just attempting to
match each device against the list. When I first implemented the table-
based quirks, back in the mists of time, there were relatively few. 

Now I wonder if it's worth sorting the list by vendor ID or something,
at least for the common case of the quirks which match on
vendor/device.

I note it's also reading PCI_CACHE_LINE_SIZE From config space for each
device in pci_apply_final_quirks(). How long does that take?
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