netdev - Re: [PATCH] Check for SKBTX_HW

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Message-ID: <CAD56B7cbPQwcsy2FTJeWKM25s-Vq=nMd=9CpXTVXLVq8ovx4cw@mail.gmail.com>
Date:   Tue, 12 Mar 2019 19:30:32 -0400
From:   Paul Thomas <pthomas8589@...il.com>
To:     "Keller, Jacob E" <jacob.e.keller@...el.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] Check for SKBTX_HW_TSTAMP in macb driver

On Tue, Mar 12, 2019 at 7:07 PM Keller, Jacob E
<jacob.e.keller@...el.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Paul Thomas [mailto:pthomas8589@...il.com]
> > Sent: Tuesday, March 12, 2019 3:05 PM
> > To: Keller, Jacob E <jacob.e.keller@...el.com>
> > Cc: netdev@...r.kernel.org
> > Subject: Re: [PATCH] Check for SKBTX_HW_TSTAMP in macb driver
> >
> > Hi Jake, thanks for all the help and for looking at this!
> >
> > >
> > > You have two conditionals inside, and I misread where you were doing the checking
> > of the SKBTX_HW_TSTAMP flag.
> > >
> > > I would do the following :
> > >
> > > if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HWTSTAMP) &&
> > >     gem_ptp_do_txstamp(queue, skb, desc)) {
> > I guess I was thinking the call to gem_ptp_do_txstamp() could be
> > avoided in many cases, but either way is fine with me..
>
> The call will be avoided by virtue of short-curcuit boolean AND. If the first check is false, then the entire section is skipped without evaluating the second condition.
Cool! good to know.

-Paul

> Thanks,
> Jake
>
> > >   ....
> > > }
> > >
> > -Paul