linux-kernel - Re: [RFC][PATCH 5/7] irq_work, smp: Allow irq_work on call_single

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Date:   Fri, 5 Jun 2020 18:17:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org, x86@...nel.org,
        cai@....pw, mgorman@...hsingularity.net, sfr@...b.auug.org.au,
        linux@...ck-us.net, keescook@...omium.org
Subject: Re: [RFC][PATCH 5/7] irq_work, smp: Allow irq_work on
 call_single_queue

On Fri, Jun 05, 2020 at 05:02:08PM +0200, Frederic Weisbecker wrote:
> On Fri, Jun 05, 2020 at 11:37:04AM +0200, Peter Zijlstra wrote:
> >  struct irq_work {
> > -	struct llist_node llnode;
> > -	atomic_t flags;
> > +	union {
> > +		struct __call_single_node node;
> > +		struct {
> > +			struct llist_node llnode;
> > +			atomic_t flags;
> > +		};
> > +	};
> 
> So why not just embed struct __call_single_node in
> struct irq_work and struct __call_single_data ?
> 
> Is the point of that anonymous second union layer to
> shorten the lines while accessing members?

To cut down on all the churn. irq_work is small and could easily be
fixed up, but csd is used in quite a few places.