Date: Sat, 9 May 2009 06:57:31 -0700
From: Greg KH <greg@kroah.com>
To: Eric Valette <eric.valette@free.fr>
Cc: Hin-Tak Leung <hintak.leung@gmail.com>,
	"John W. Linville" <linville@tuxdriver.com>,
	linux-wireless@vger.kernel.org,
	Larry Finger <Larry.Finger@lwfinger.net>,
	FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
	linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org
Subject: Re: [RFT] rtl8187: use DMA-aware buffers with usb_control_msg
Message-ID: <20090509135731.GD17349@kroah.com>
References: <20090506064513.GA7460@kroah.com> <1241632963-25601-1-git-send-email-linville@tuxdriver.com> <3ace41890905081620h10d0250eq1ede9cd73021dc5b@mail.gmail.com> <4A054F18.7020501@free.fr>
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In-Reply-To: <4A054F18.7020501@free.fr>
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On Sat, May 09, 2009 at 11:38:32AM +0200, Eric Valette wrote:
> The patch fix the DMA warning and the driver seems to work (just
> associated it) but I must say that the allocation failure handling path
> and the fact that we use now kmalloc for allocating a few bytes in such
> a routine makes me worry about possible negative performance impact
> unless theses routines are used only in a slow configuration path (did
> no took time to red the code due to many other problems).

usb_control messages are slow and should not be on the "fast path" of
any data being sent through the device.  Any overhead of the
kmalloc/kfree is totally eaten up by the actual transmission turn around
time of the message itself, so you don't have to worry about the
performance impact.

thanks for testing.

> BTW if someone know who I should send this attached patch for DRM git, I
> would gladly forward it.

To the drm maintainer?

thanks,

greg k-h