netdev - RE: [PATCH v2] ice: use min_t() to make code cleaner in ice

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Date:   Tue, 22 Mar 2022 18:12:08 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alexander Lobakin' <alexandr.lobakin@...el.com>
CC:     'Wan Jiabing' <wanjiabing@...o.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] ice: use min_t() to make code cleaner in ice_gnss

From: Alexander Lobakin
> Sent: 22 March 2022 17:51
> From: David Laight <David.Laight@...LAB.COM>
> Date: Mon, 21 Mar 2022 16:02:20 +0000
> 
> > From: Wan Jiabing
> > > Sent: 21 March 2022 14:00
> > >
> > > Fix the following coccicheck warning:
> > > ./drivers/net/ethernet/intel/ice/ice_gnss.c:79:26-27: WARNING opportunity for min()
> > >
> > > Signed-off-by: Wan Jiabing <wanjiabing@...o.com>
> > > ---
> > > Changelog:
> > > v2:
> > > - Use typeof(bytes_left) instead of u8.
> > > ---
> > >  drivers/net/ethernet/intel/ice/ice_gnss.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/intel/ice/ice_gnss.c b/drivers/net/ethernet/intel/ice/ice_gnss.c
> > > index 35579cf4283f..57586a2e6dec 100644
> > > --- a/drivers/net/ethernet/intel/ice/ice_gnss.c
> > > +++ b/drivers/net/ethernet/intel/ice/ice_gnss.c
> > > @@ -76,8 +76,7 @@ static void ice_gnss_read(struct kthread_work *work)
> > >  	for (i = 0; i < data_len; i += bytes_read) {
> > >  		u16 bytes_left = data_len - i;
> >
> > Oh FFS why is that u16?
> > Don't do arithmetic on anything smaller than 'int'
> 
> Any reasoning? I don't say it's good or bad, just want to hear your
> arguments (disasms, perf and object code measurements) etc.

Look at the object code on anything except x86.
The compiler has to add instruction to mask the value
(which is in a full sized register) down to 16 bits
after every arithmetic operation.

	David

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