linux-kernel - Re: [PATCH] dma: fix vchan_cookie

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Date:	Mon, 20 Jan 2014 13:28:29 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	Jonas Jensen <jonas.jensen@...il.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	arm@...nel.org, dan.j.williams@...el.com
Subject: Re: [PATCH] dma: fix vchan_cookie_complete() debug print

On Mon, Jan 20, 2014 at 05:33:01PM +0530, Vinod Koul wrote:
> On Mon, Jan 20, 2014 at 11:28:22AM +0000, Russell King - ARM Linux wrote:
> > On Mon, Jan 20, 2014 at 03:29:17PM +0530, Vinod Koul wrote:
> > > On Fri, Dec 06, 2013 at 04:42:09PM +0100, Jonas Jensen wrote:
> > > > vd->tx.cookie is set zero on dma_cookie_complete(),
> > > > save to local before printing it.
> > > > 
> > > > Signed-off-by: Jonas Jensen <jonas.jensen@...il.com>
> > > > ---
> > > > 
> > > > Notes:
> > > >     dev_vdbg() could also be moved to happen earlier, what do you prefer?
> > > This would be preferred IMHO. Also pls cc dmaengine@...r on this
> > 
> > I prefer this version - it means that the verbose debug printk doesn't
> > impact the completion timing when printk is expensive (eg, because its
> > outputting via a serial port.)
> But if you know your printk is costly, do you want to enable these?

dev_vdbg() is for verbose debugging - you only enable it if you really
need to.  Even so, it should have _minimal_ impact where possible.  That's
why I prefer the first patch, because we mark the cookie as being
complete _before_ we call the verbose debugging, which isn't going to add
milliseconds to that.

If you don't care about debugging, then getting rid of the dev_vdbg().
But really, I could pull rank and say that this is *my* file, I get to
choose how stuff should be done here - I'd prefer not to but...

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