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From: Alan Stern <stern@rowland.harvard.edu>
To: Doug Anderson <dianders@chromium.org>
Cc: "John Youn" <John.Youn@synopsys.com>,
	"Felipe Balbi" <balbi@ti.com>, "Yunzhi Li" <lyz@rock-chips.com>,
	"Heiko Stübner" <heiko@sntech.de>,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	"Julius Werner" <jwerner@chromium.org>,
	"Herrero, Gregory" <gregory.herrero@intel.com>,
	"Kaukab, Yousaf" <yousaf.kaukab@intel.com>,
	"Dinh Nguyen" <dinguyen@opensource.altera.com>,
	"John Youn" <johnyoun@synopsys.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Ming Lei" <ming.lei@canonical.com>
Subject: Re: [PATCH 2/3] usb: dwc2: host: Giveback URB in tasklet context
Date: Thu, 5 Nov 2015 10:19:00 -0500 (EST)	[thread overview]
Message-ID: <Pine.LNX.4.44L0.1511051012580.25468-100000@netrider.rowland.org> (raw)
In-Reply-To: <CAD=FV=WhD-CcHHZN0_h57xPmvwiOiroOQKoDpy8f2HfDJY-PCg@mail.gmail.com>

On Wed, 4 Nov 2015, Doug Anderson wrote:

> In the ChromeOS gerrit
> <https://chromium-review.googlesource.com/#/c/310583/> Julius Werner
> points out that for EHCI it was good to take the optimization from
> commit 9118f9eb4f1e ("USB: EHCI: improve interrupt qh unlink") before
> this one.  I'm still trying to learn USB / dwc2 so it's unclear to me
> whether we also need a similar change before landing.
> 
> I'll see if I can do some investigation about this and also some
> benchmarking before and after.  Certainly profiling the interrupt
> handler itself showed a huge improvement, but I'd hate to see a
> regression elsewhere.
> 
> If anyone else knows better than I, please speak up!  :)

This is a matter of both efficiency and correctness.  Giving back URBs 
in a tasklet is not a simple change.

Have you read the kerneldoc for usb_submit_urb() in 
drivers/usb/core/urb.c?  The portion about "Reserved Bandwidth 
Transfers" is highly relevant.  I don't know how dwc2 goes about 
reserving bandwidth for periodic transfers, but if it relies on the 
endpoint queue being non-empty to maintain a reservation then it will 
be affected by this change.

Alan Stern


  reply	other threads:[~2015-11-05 15:19 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-11-04 22:53 [PATCH 0/3] dwc2: Speed up the interrupt handler quite a bit Douglas Anderson
2015-11-04 22:53 ` Douglas Anderson
2015-11-04 22:53 ` [PATCH 1/3] usb: dwc2: rockchip: Make the max_transfer_size automatic Douglas Anderson
2015-11-04 22:53 ` [PATCH 2/3] usb: dwc2: host: Giveback URB in tasklet context Douglas Anderson
2015-11-04 22:53   ` Douglas Anderson
2015-11-05  0:30   ` Doug Anderson
2015-11-05  0:30     ` Doug Anderson
2015-11-05 15:19     ` Alan Stern [this message]
2015-11-06  0:29       ` Doug Anderson
2015-11-06 15:40         ` Alan Stern
2015-11-07  1:26           ` Doug Anderson
2015-11-07 15:09             ` Alan Stern
2015-11-04 22:53 ` [PATCH 3/3] usb: dwc2: host: Get aligned DMA in a more supported way Douglas Anderson
2015-11-05 19:18 ` [PATCH 0/3] dwc2: Speed up the interrupt handler quite a bit Heiko Stuebner
2015-11-05 19:18   ` Heiko Stuebner

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