On Tue, 8 Dec 2020 16:11:14 +0100
Cédric Le Goater <c...@kaod.org> wrote:
> The XIVE driver deals with CPU IPIs in a peculiar way. Each CPU has
> its own XIVE IPI interrupt allocated at the HW level, for PowerNV, or
> at the hypervisor level for pSeries. In practice, these interrupts are
> not always used. pSeries/PowerVM prefers local doorbells for local
> threads since they are faster. On PowerNV, global doorbells are also
> preferred for the same reason.
>
> The mapping in the Linux is reduced to a single interrupt using HW
> interrupt number 0 and a custom irq_chip to handle EOI. This can cause
> performance issues in some benchmark (ipistorm) on multichip systems.
>
> Clarify the use of the 0 value, it will help in improving multichip
> support.
>
> Signed-off-by: Cédric Le Goater <c...@kaod.org>
> ---
Reviewed-by: Greg Kurz <gr...@kaod.org>
> arch/powerpc/sysdev/xive/xive-internal.h | 2 ++
> arch/powerpc/sysdev/xive/common.c | 10 +++++-----
> 2 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/arch/powerpc/sysdev/xive/xive-internal.h
> b/arch/powerpc/sysdev/xive/xive-internal.h
> index b7b901da2168..d701af7fb48c 100644
> --- a/arch/powerpc/sysdev/xive/xive-internal.h
> +++ b/arch/powerpc/sysdev/xive/xive-internal.h
> @@ -5,6 +5,8 @@
> #ifndef __XIVE_INTERNAL_H
> #define __XIVE_INTERNAL_H
>
> +#define XIVE_IPI_HW_IRQ 0 /* interrupt source # for IPIs */
> +
> /*
> * A "disabled" interrupt should never fire, to catch problems
> * we set its logical number to this
> diff --git a/arch/powerpc/sysdev/xive/common.c
> b/arch/powerpc/sysdev/xive/common.c
> index 65af34ac1fa2..ee375daf8114 100644
> --- a/arch/powerpc/sysdev/xive/common.c
> +++ b/arch/powerpc/sysdev/xive/common.c
> @@ -1142,7 +1142,7 @@ static void __init xive_request_ipi(void)
> return;
>
> /* Initialize it */
> - virq = irq_create_mapping(xive_irq_domain, 0);
> + virq = irq_create_mapping(xive_irq_domain, XIVE_IPI_HW_IRQ);
> xive_ipi_irq = virq;
>
> WARN_ON(request_irq(virq, xive_muxed_ipi_action,
> @@ -1242,7 +1242,7 @@ static int xive_irq_domain_map(struct irq_domain *h,
> unsigned int virq,
>
> #ifdef CONFIG_SMP
> /* IPIs are special and come up with HW number 0 */
> - if (hw == 0) {
> + if (hw == XIVE_IPI_HW_IRQ) {
> /*
> * IPIs are marked per-cpu. We use separate HW interrupts under
> * the hood but associated with the same "linux" interrupt
> @@ -1271,7 +1271,7 @@ static void xive_irq_domain_unmap(struct irq_domain *d,
> unsigned int virq)
> if (!data)
> return;
> hw_irq = (unsigned int)irqd_to_hwirq(data);
> - if (hw_irq)
> + if (hw_irq != XIVE_IPI_HW_IRQ)
> xive_irq_free_data(virq);
> }
>
> @@ -1421,7 +1421,7 @@ static void xive_flush_cpu_queue(unsigned int cpu,
> struct xive_cpu *xc)
> * Ignore anything that isn't a XIVE irq and ignore
> * IPIs, so can just be dropped.
> */
> - if (d->domain != xive_irq_domain || hw_irq == 0)
> + if (d->domain != xive_irq_domain || hw_irq == XIVE_IPI_HW_IRQ)
> continue;
>
> /*
> @@ -1655,7 +1655,7 @@ static int xive_core_debug_show(struct seq_file *m,
> void *private)
> hw_irq = (unsigned int)irqd_to_hwirq(d);
>
> /* IPIs are special (HW number 0) */
> - if (hw_irq)
> + if (hw_irq != XIVE_IPI_HW_IRQ)
> xive_debug_show_irq(m, hw_irq, d);
> }
> return 0;
