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From: Duncan Sands <baldrick@free.fr>
To: Oliver Neukum <oliver@neukum.org>, Greg KH <greg@kroah.com>
Subject: Re: [linux-usb-devel] [PATCH 1/9] USB usbfs: take a reference to the usb device
Date: Sun, 18 Apr 2004 16:08:21 +0200
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Cc: linux-usb-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org,
       Frederic Detienne <fd@cisco.com>
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Hi Oliver,

> Multiple interfaces are uncommon. Devices with several interfaces bound
> to usbfs are uncommoner. Concurrent use is still uncommoner. You are
> slowing the common case.

The slowdown is probably negligeable though.  The speedup may be big for
the rare cases where it matters (though I doubt anyone is ever going to care
one way or the other).

> > > > (2) push the acquisition of dev->serialize down to the lower levels
> > > > as they are fixed up.
> > >
> > > Why?
> >
> > Efficiency.  The main reason is that the copy to/from user calls are
> > inside the locked region :) As for the other places where the lock could
> > be dropped, I guess measurement is required to see if it gains anything.
>
> OK. I see. But IMHO usbfs is not written for speed anyway, so don't
> worry too much.

I'm not worrying!  It's more a matter of hygiene :)

Duncan.