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From: Greg KH <gregkh@linuxfoundation.org>
To: David Miller <davem@davemloft.net>
Cc: hayeswang@realtek.com, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
	nic_swsd@realtek.com
Subject: Re: [PATCH v3 1/3] net/usb/r815x: replace USB buffer from stack to DMA-able
Date: Tue, 30 Jul 2013 11:58:08 -0700	[thread overview]
Message-ID: <20130730185808.GA25353@kroah.com> (raw)
In-Reply-To: <20130730.113329.1450325193505423812.davem@davemloft.net>

On Tue, Jul 30, 2013 at 11:33:29AM -0700, David Miller wrote:
> From: Greg KH <gregkh@linuxfoundation.org>
> Date: Tue, 30 Jul 2013 07:00:59 -0700
> 
> > This call is so slow, you can afford to make a call to kmalloc for the
> > data, as it sure just did for other structures it needed :)
> 
> I told him to implement things this way, to avoid calling kmalloc every
> single register access.
> 
> Using kmalloc all the time makes the access fragile, since a badly timed
> call during high memory pressure can fail.
> 
> I'd rather the potential failure happen at one time, probe time.

I agree, but the call usb_control_message() also does a tiny kmalloc(),
and is _very_ slow and if you have high memory pressure, doing USB
messages like this is not what you want to do anyway (the host
controller does it's own allocations and the like as well.)

USB isn't "fast" like most normal networking physical layers :)

thanks,

greg k-h

  parent reply	other threads:[~2013-07-30 18:58 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-23  9:26 [PATCH 1/3] net/usb/r815x: replace USB buffer from stack to DMA-able hayeswang
2013-07-25  0:49 ` David Miller
2013-07-25  7:59   ` [PATCH v2 " Hayes Wang
2013-07-25  7:59     ` [PATCH v2 2/3] net/usb/r8152: make sure the USB buffer is DMA-able Hayes Wang
2013-07-25  7:59     ` [PATCH v2 3/3] net/usb/r8152: adjust relative ocp function Hayes Wang
     [not found]     ` <1374739144-732-1-git-send-email-hayeswang-Rasf1IRRPZFBDgjK7y7TUQ@public.gmane.org>
2013-07-28  3:21       ` [PATCH v2 1/3] net/usb/r815x: replace USB buffer from stack to DMA-able David Miller
2013-07-29  5:20         ` Oliver Neukum
2013-07-29  7:46           ` David Miller
2013-07-30  8:28 ` [PATCH v3 " Hayes Wang
2013-07-30  8:28   ` [PATCH v3 2/3] net/usb/r8152: " Hayes Wang
2013-07-30 14:01     ` Greg KH
2013-07-30  8:28   ` [PATCH v3 3/3] net/usb/r8152: adjust relative ocp function Hayes Wang
2013-07-30 13:58   ` [PATCH v3 1/3] net/usb/r815x: replace USB buffer from stack to DMA-able Greg KH
2013-07-30 15:17     ` [PATCH] MAINTAINERS: USB, remove F: drivers/net/usb/ pattern Joe Perches
2013-07-30 14:00   ` [PATCH v3 1/3] net/usb/r815x: replace USB buffer from stack to DMA-able Greg KH
2013-07-30 18:33     ` David Miller
2013-07-30 18:41       ` Joe Perches
2013-07-30 18:49         ` David Miller
2013-07-31 10:29           ` Ming Lei
2013-07-30 18:58       ` Greg KH [this message]
2013-07-30 14:29   ` Ming Lei
2013-07-31  9:21 ` [PATCH v4 1/5] " Hayes Wang
2013-07-31  9:21   ` [PATCH v4 2/5] net/usb/r815x: avoid to call mdio functions for runtime-suspended device Hayes Wang
2013-07-31 21:49     ` David Miller
2013-07-31  9:21   ` [PATCH v4 3/5] net/usb/r815x: change the return value for bind functions Hayes Wang
     [not found]     ` <1375262486-5373-3-git-send-email-hayeswang-Rasf1IRRPZFBDgjK7y7TUQ@public.gmane.org>
2013-07-31 21:49       ` David Miller
     [not found]   ` <1375262486-5373-1-git-send-email-hayeswang-Rasf1IRRPZFBDgjK7y7TUQ@public.gmane.org>
2013-07-31  9:21     ` [PATCH v4 4/5] net/usb/r8152: make sure the USB buffer is DMA-able Hayes Wang
2013-07-31 12:54       ` Greg KH
2013-07-31 21:50       ` David Miller
2013-07-31  9:21   ` [PATCH v4 5/5] net/usb/r8152: adjust relative ocp function Hayes Wang
2013-07-31 21:50     ` David Miller
2013-07-31 12:53   ` [PATCH v4 1/5] net/usb/r815x: replace USB buffer from stack to DMA-able Greg KH
2013-07-31 21:49   ` David Miller

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