linux-kernel - Re: [PATCH RESEND][pciutils] libpci: pci_id_lookup

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Message-ID: <CAPXgP10+1WtX8_xN+QSHvKws01hbKhP3FN95sXk9EtezdSPtqg@mail.gmail.com>
Date:	Sun, 15 Dec 2013 10:49:24 +0100
From:	Kay Sievers <kay@...y.org>
To:	Martin Mares <mj@....cz>
Cc:	Tom Gundersen <teg@...m.no>, LKML <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH RESEND][pciutils] libpci: pci_id_lookup - add udev/hwdb support

On Sun, Dec 15, 2013 at 10:18 AM, Martin Mares <mj@....cz> wrote:
> Hello Kay,
>
>> Libpci and its linear search through megabytes of text files for evey
>> new query is too inefficient, that we cannot afford to use it during
>> early bootup. It was the largest hit left in bootup profiling on
>> machines booting userspace in the sub-1-second range on common
>> machines. It was probably never meant to provide efficient queries,
>> but it's the reason we can never use it during early boot.
>
> I do not know what you are speaking about -- libpci definitely does
> not perform linear scans on pci.ids. It builds a hash table from pci.ids
> on the first query and and all subsequent queries are O(1) on average.

It does that per process doing that, and that's the problem for how
udev works/worked. The binary hwdb is on-disk and can be mmaped, and
there is no difference between initialization, first, or subsequent
queries.

Kay
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