linux-kernel - Re: [PATCH] RISC-V: Show IPI stats

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Date:   Mon, 01 Oct 2018 09:42:37 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     anup@...infault.org
CC:     Christoph Hellwig <hch@...radead.org>, aou@...s.berkeley.edu,
        atish.patra@....com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject:     Re: [PATCH] RISC-V: Show IPI stats

On Fri, 28 Sep 2018 23:09:56 PDT (-0700), anup@...infault.org wrote:
> On Sat, Sep 29, 2018 at 7:15 AM Palmer Dabbelt <palmer@...ive.com> wrote:
>>
>> On Mon, 10 Sep 2018 06:46:59 PDT (-0700), Christoph Hellwig wrote:
>> > On Fri, Sep 07, 2018 at 06:14:29PM +0530, Anup Patel wrote:
>> >> This patch provides arch_show_interrupts() implementation to
>> >> show IPI stats via /proc/interrupts.
>> >>
>> >> Now the contents of /proc/interrupts" will look like below:
>> >>            CPU0       CPU1       CPU2       CPU3
>> >>   8:         17          7          6         14  SiFive PLIC   8  virtio0
>> >>  10:         10         10          9         11  SiFive PLIC  10  ttyS0
>> >> IPI0:       170        673        251         79  Rescheduling interrupts
>> >> IPI1:         1         12         27          1  Function call interrupts
>> >> IPI2:         0          0          0          0  CPU wake-up interrupts
>> >>
>> >> Signed-off-by: Anup Patel <anup@...infault.org>
>> >
>> > Thanks, this looks pretty sensible to me.  Maybe we want to also show
>> > timer interrupts if we do this?
>>
>> IIRC we used to have some issue where the timer interrupt ID in
>> /proc/interrupts aliased with a possible PLIC interrupt ID, but that was back
>> when we had a big mess of chained interrupt drivers that didn't really talk to
>> each other.  I think at some point I might have just removed the timer
>> interrupt from /proc/interrupts as a hack, but now that our interrupt
>> controller mess is sorted out it'd be better to have it.
>
> If we have irqdomain and irqchip for HLIC then showing timer interrupts
> becomes cleaner. My RISCV INTC patch achieves this.
>
>>
>> I'm fine taking this without the timer interrupts, as something is better than
>> nothing.
>
> Sure.
>
>>
>> >> --- a/arch/riscv/kernel/irq.c
>> >> +++ b/arch/riscv/kernel/irq.c
>> >> @@ -8,6 +8,7 @@
>> >>  #include <linux/interrupt.h>
>> >>  #include <linux/irqchip.h>
>> >>  #include <linux/irqdomain.h>
>> >> +#include <linux/seq_file.h>
>> >>
>> >>  /*
>> >>   * Possible interrupt causes:
>> >> @@ -24,6 +25,14 @@
>> >>   */
>> >>  #define INTERRUPT_CAUSE_FLAG        (1UL << (__riscv_xlen - 1))
>> >>
>> >> +int arch_show_interrupts(struct seq_file *p, int prec)
>> >> +{
>> >> +#ifdef CONFIG_SMP
>> >> +    show_ipi_stats(p, prec);
>> >> +#endif
>> >> +    return 0;
>> >> +}
>> >
>> > If we don't also add timer stats I'd just move arch_show_interrupts
>> > to smp.c and make it conditional.  If we don't this split might make
>> > more sense.
>>
>> Makes sense, but I think timer interrupts are more interesting to see than IPIs
>> so we'll eventually pipe them through.  Might just be my workloads, though :)
>>
>> >> +static const char *ipi_names[IPI_MAX] = {
>> >> +    [IPI_RESCHEDULE] = "Rescheduling interrupts",
>> >> +    [IPI_CALL_FUNC] = "Function call interrupts",
>> >> +    [IPI_CALL_WAKEUP] = "CPU wake-up interrupts",
>> >> +};
>> >
>> > No need for the explicit array size.  Also please use a few tabs to
>> > align this nicely:
>> >
>> > static const char *ipi_names[] = {
>> >       [IPI_RESCHEDULE]        = "Rescheduling interrupts",
>> >       [IPI_CALL_FUNC]         = "Function call interrupts",
>> >       [IPI_CALL_WAKEUP]       = "CPU wake-up interrupts",
>> > };
>>
>> I don't see a v2 of this, was there one?  If not then I'll just clean up
>> ipi_names and drop this on for-next.
>>
>> Thanks for the patch!
>
> I will send v3 patch because IPI_CALL_WAKEUP is not going to be available.
>
> I will base v3 patch upon v5 of Atish's patchset. Atish will take v3 of this
> patch and make it part of his v6 patchset so that it will be easy for you
> to apply.

Thanks!