From: Stefano Stabellini <sstabellini@kernel.org>
To: Jan Beulich <jbeulich@suse.com>
Cc: Julien Grall <julien@xen.org>,
bertrand.marquis@arm.com, Rahul.Singh@arm.com,
Julien Grall <jgrall@amazon.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
Ian Jackson <iwj@xenproject.org>,
Stefano Stabellini <sstabellini@kernel.org>,
Wei Liu <wl@xen.org>,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH] xen: Rework WARN_ON() to return whether a warning was triggered
Date: Thu, 17 Dec 2020 15:54:45 -0800 (PST) [thread overview]
Message-ID: <alpine.DEB.2.21.2012171553340.4040@sstabellini-ThinkPad-T480s> (raw)
In-Reply-To: <3f165cf8-88a4-590a-6e86-2435e8a7e554@suse.com>
On Tue, 15 Dec 2020, Jan Beulich wrote:
> On 15.12.2020 14:19, Julien Grall wrote:
> > On 15/12/2020 11:46, Jan Beulich wrote:
> >> On 15.12.2020 12:26, Julien Grall wrote:
> >>> --- a/xen/include/xen/lib.h
> >>> +++ b/xen/include/xen/lib.h
> >>> @@ -23,7 +23,13 @@
> >>> #include <asm/bug.h>
> >>>
> >>> #define BUG_ON(p) do { if (unlikely(p)) BUG(); } while (0)
> >>> -#define WARN_ON(p) do { if (unlikely(p)) WARN(); } while (0)
> >>> +#define WARN_ON(p) ({ \
> >>> + bool __ret_warn_on = (p); \
> >>
> >> Please can you avoid leading underscores here?
> >
> > I can.
> >
> >>
> >>> + \
> >>> + if ( unlikely(__ret_warn_on) ) \
> >>> + WARN(); \
> >>> + unlikely(__ret_warn_on); \
> >>> +})
> >>
> >> Is this latter unlikely() having any effect? So far I thought it
> >> would need to be immediately inside a control construct or be an
> >> operand to && or ||.
> >
> > The unlikely() is directly taken from the Linux implementation.
> >
> > My guess is the compiler is still able to use the information for the
> > branch prediction in the case of:
> >
> > if ( WARN_ON(...) )
>
> Maybe. Or maybe not. I don't suppose the Linux commit introducing
> it clarifies this?
I did a bit of digging but it looks like the unlikely has been there
forever. I'd just keep it as is.
next prev parent reply other threads:[~2020-12-17 23:55 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-15 11:26 [PATCH] xen: Rework WARN_ON() to return whether a warning was triggered Julien Grall
2020-12-15 11:31 ` Jürgen Groß
2020-12-15 13:11 ` Julien Grall
2020-12-15 16:20 ` Jürgen Groß
2020-12-17 17:58 ` Bertrand Marquis
2020-12-15 11:46 ` Jan Beulich
2020-12-15 13:19 ` Julien Grall
2020-12-15 14:01 ` Jan Beulich
2020-12-17 23:54 ` Stefano Stabellini [this message]
2020-12-18 0:29 ` Julien Grall
2020-12-18 7:54 ` Jan Beulich
2020-12-18 8:19 ` Jürgen Groß
2020-12-18 8:31 ` Jan Beulich
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