linux-kernel - Re: [PATCH] atl1c: optimize rx loop

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Message-ID: <20210322005326.GA24403@DESKTOP-8REGVGF.localdomain>
Date:   Mon, 22 Mar 2021 08:54:01 +0800
From:   Sieng Piaw Liew <liew.s.piaw@...il.com>
To:     Willy Tarreau <w@....eu>
Cc:     chris.snook@...il.com, davem@...emloft.net, kuba@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] atl1c: optimize rx loop

On Fri, Mar 19, 2021 at 05:15:35AM +0100, Willy Tarreau wrote:
> On Fri, Mar 19, 2021 at 12:04:47PM +0800, Sieng Piaw Liew wrote:
> > Remove this trivial bit of inefficiency from the rx receive loop,
> > results in increase of a few Mbps in iperf3. Tested on Intel Core2
> > platform.
> > 
> > Signed-off-by: Sieng Piaw Liew <liew.s.piaw@...il.com>
> > ---
> >  drivers/net/ethernet/atheros/atl1c/atl1c_main.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> > index 3f65f2b370c5..b995f9a0479c 100644
> > --- a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> > +++ b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> > @@ -1796,9 +1796,7 @@ static void atl1c_clean_rx_irq(struct atl1c_adapter *adapter,
> >  	struct atl1c_recv_ret_status *rrs;
> >  	struct atl1c_buffer *buffer_info;
> >  
> > -	while (1) {
> > -		if (*work_done >= work_to_do)
> > -			break;
> > +	while (*work_done < work_to_do) {
> 
> It should not change anything, or only based on the compiler's optimization
> and should not result in a measurable difference because what it does is
> exactly the same. Have you really compared the compiled output code to
> explain the difference ? I strongly suspect you'll find no difference at
> all.
> 
> Thus for me it's certainly not an optimization, it could be qualified as
> a cleanup to improve code readability however.
> 
> Willy

You're right. Objdump and diff showed no difference.

Regards,
Sieng Piaw