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SubjectRe: [PATCH tip/core/rcu 2/4] smp: Add source and destination CPUs to __call_single_data
Hi Paul,

On Mon, Aug 31, 2020 at 11:14:15AM -0700, paulmck@kernel.org wrote:
> From: "Paul E. McKenney" <paulmck@kernel.org>
>
> This commit adds a destination CPU to __call_single_data, and is inspired
> by an earlier commit by Peter Zijlstra. This version adds #ifdef to
> permit use by 32-bit systems and supplying the destination CPU for all
> smp_call_function*() requests, not just smp_call_function_single().
>
> If need be, 32-bit systems could be accommodated by shrinking the flags
> field to 16 bits (the atomic_t variant is currently unused) and by
> providing only eight bits for CPU on such systems.
>
> It is not clear that the addition of the fields to __call_single_node
> are really needed.
>
> Link: https://lore.kernel.org/lkml/20200615164048.GC2531@hirez.programming.kicks-ass.net/
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: Frederic Weisbecker <frederic@kernel.org>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> ---
> include/linux/smp.h | 3 +++
> include/linux/smp_types.h | 3 +++
> kernel/smp.c | 2 ++
> 3 files changed, 8 insertions(+)
>
> diff --git a/include/linux/smp.h b/include/linux/smp.h
> index 80d557e..9f13966 100644
> --- a/include/linux/smp.h
> +++ b/include/linux/smp.h
> @@ -26,6 +26,9 @@ struct __call_single_data {
> struct {
> struct llist_node llist;
> unsigned int flags;
> +#ifdef CONFIG_64BIT
> + u16 src, dst;
> +#endif
> };
> };
> smp_call_func_t func;
> diff --git a/include/linux/smp_types.h b/include/linux/smp_types.h
> index 364b3ae..2e8461a 100644
> --- a/include/linux/smp_types.h
> +++ b/include/linux/smp_types.h
> @@ -61,6 +61,9 @@ struct __call_single_node {
> unsigned int u_flags;
> atomic_t a_flags;
> };
> +#ifdef CONFIG_64BIT
> + u16 src, dst;
> +#endif
> };
>
> #endif /* __LINUX_SMP_TYPES_H */
> diff --git a/kernel/smp.c b/kernel/smp.c
> index d0ae8eb..a47382d 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -375,6 +375,7 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
>
> csd->func = func;
> csd->info = info;
> + csd->dst = cpu;

Would this and the next modification cause compile errors with
CONFIG_64BIT = n? I saw you add #ifdef guard in the next patch, so maybe
move those two into next patch (of course, if they trigger compile
errors)

Regards,
Boqun

>
> err = generic_exec_single(cpu, csd);
>
> @@ -540,6 +541,7 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
> csd->flags |= CSD_TYPE_SYNC;
> csd->func = func;
> csd->info = info;
> + csd->dst = cpu;
> if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))
> __cpumask_set_cpu(cpu, cfd->cpumask_ipi);
> }
> --
> 2.9.5
>

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