linux-kernel - Re: [PATCH] ttyprintk: optimize tpk

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Date:   Thu, 12 Nov 2020 21:41:22 +0800
From:   sunjunyong <sunjy516@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     arnd@...db.de, sunjunyong@...omi.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ttyprintk: optimize tpk_close flush code

Hi Greg:
It have no logic that handles NULL in tpk_flush() but tpk_printk().
Do you mean that if i understand correctly?!I think we should not remove 
the logic that handles NULL in tpk_printk() as we don't know if the buf 
from parent caller is null or not.But we transfer a null buf to tpk_printk()
 for previous version of tpk_close, i think it's redundant.

The comment is a hitory tip for other guys to understand.I suggest to 
keep it as before if you like.

thanks
JY
On Thu, Nov 12, 2020 at 08:52:23AM +0100, Greg KH wrote:
> On Wed, Nov 04, 2020 at 02:02:24PM +0800, Junyong Sun wrote:
> > tpk_printk(NULL,0) do nothing but call tpk_flush to
> > flush buffer, so why don't use tpk_flush diretcly?
> > this is a small optimization.
> > 
> > Signed-off-by: Junyong Sun <sunjunyong@...omi.com>
> > ---
> >  drivers/char/ttyprintk.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/char/ttyprintk.c b/drivers/char/ttyprintk.c
> > index 6a0059e..2ce78b3 100644
> > --- a/drivers/char/ttyprintk.c
> > +++ b/drivers/char/ttyprintk.c
> > @@ -104,7 +104,7 @@ static void tpk_close(struct tty_struct *tty, struct file *filp)
> >  
> >  	spin_lock_irqsave(&tpkp->spinlock, flags);
> >  	/* flush tpk_printk buffer */
> > -	tpk_printk(NULL, 0);
> > +	tpk_flush();
> 
> If you do this, then please remove the logic in tpk_flush() that handles
> NULL as now that logic will not be needed at all, right?
> 
> Also the comment here wouldn't be needed as the code obviously does that
> based on the function call being made :)
> 
> thanks,
> 
> greg k-h