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Re: [PATCH v3 1/6] xen: add reference counter support
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 16 Mar 2023 17:21:31 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Thu, 16 Mar 2023 16:21:54 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu, Mar 16, 2023 at 03:03:42PM +0100, Jan Beulich wrote:
> On 16.03.2023 14:54, Roger Pau Monné wrote:
> > On Tue, Mar 14, 2023 at 08:56:29PM +0000, Volodymyr Babchuk wrote:
> >> +{
> >> + return atomic_read(&refcnt->refcnt);
> >> +}
> >> +
> >> +static inline void refcnt_get(refcnt_t *refcnt)
> >> +{
> >> + int old = atomic_add_unless(&refcnt->refcnt, 1, 0);
> >> +
> >> + if ( unlikely(old < 0) || unlikely (old + 1 < 0) )
> > ^ extra space
> >
> > You want a single unlikely for both conditions.
>
> Are you sure? My experience was generally the other way around: likely()
> and unlikely() become ineffectual as soon as the compiler needs more
> than one branch for the inner construct (ie generally for and && or ||).
Oh, OK, never mind then. We have examples of both in the code base.
Roger.
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