linux-kernel - Re: [PATCH 1/2] USB: EHCI: Move sysfs related bits into ehci-sysfs.c

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Message-ID: <Pine.LNX.4.44L0.1106291333440.2064-100000@iolanthe.rowland.org>
Date:	Wed, 29 Jun 2011 13:35:04 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Kirill Smelkov <kirr@....spb.ru>
cc:	matt mooney <mfm@...eddisk.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] USB: EHCI: Move sysfs related bits into ehci-sysfs.c

On Wed, 29 Jun 2011, Kirill Smelkov wrote:

> > Also, when decreasing the schedule limit, do you think it is really 
> > necessary to check that the current allocation doesn't exceed the new 
> > limit?  I think it would be sufficient to apply the new limit just to 
> > new bandwidth allocation requests.  After all, this API is meant for 
> > experts only.
> 
> I think yes, it is needed. E.g. because there is this check in
> periodic_usecs():
> 
> #ifdef  DEBUG
>         if (usecs > ehci->uframe_periodic_max)
>                 ehci_err (ehci, "uframe %d sched overrun: %d usecs\n",
>                         frame * 8 + uframe, usecs);
> #endif
>         return usecs;
> }
> 
> and periodic_usecs() is called in e.g. this chain:
> 
>     itd_submit
>     iso_stream_schedule
>     itd_slot_ok
>     periodic_usecs
> 
> and others.

That won't matter unless DEBUG is defined.

> I'd leave this check as is - to me it would be useful in debug mode to
> verify that we've not overallocated a period.
> 
> Also, even if this knob would be useful only to experts, it would be
> better to put feedback onto the knob so that people could know whether
> thir request could be served or not.
> 
> What do you think?

Can you make that check conditional on DEBUG being set?

Alan Stern

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