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Message-Id: <27744344-f4f3-0952-94e2-d80071a137a7@de.ibm.com>
Date: Mon, 11 Dec 2017 15:35:02 +0100
From: Christian Borntraeger <borntraeger@...ibm.com>
To: Yury Norov <ynorov@...iumnetworks.com>,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Ashish Kalra <Ashish.Kalra@...ium.com>,
Christoffer Dall <christoffer.dall@...aro.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Linu Cherian <Linu.Cherian@...ium.com>,
Sunil Goutham <Sunil.Goutham@...ium.com>
Subject: Re: [PATCH] IPI performance benchmark
On 12/11/2017 03:16 PM, Yury Norov wrote:
> This benchmark sends many IPIs in different modes and measures
> time for IPI delivery (first column), and total time, ie including
> time to acknowledge the receive by sender (second column).
>
> The scenarios are:
> Dry-run: do everything except actually sending IPI. Useful
> to estimate system overhead.
> Self-IPI: Send IPI to self CPU.
> Normal IPI: Send IPI to some other CPU.
> Broadcast IPI: Send broadcast IPI to all online CPUs.
>
> For virtualized guests, sending and reveiving IPIs causes guest exit.
> I used this test to measure performance impact on KVM subsystem of
> Christoffer Dall's series "Optimize KVM/ARM for VHE systems".
>
> https://www.spinics.net/lists/kvm/msg156755.html
>
> Test machine is ThunderX2, 112 online CPUs. Below the results normalized
> to host dry-run time. Smaller - better.
>
> Host, v4.14:
> Dry-run: 0 1
> Self-IPI: 9 18
> Normal IPI: 81 110
> Broadcast IPI: 0 2106
>
> Guest, v4.14:
> Dry-run: 0 1
> Self-IPI: 10 18
> Normal IPI: 305 525
> Broadcast IPI: 0 9729
>
> Guest, v4.14 + VHE:
> Dry-run: 0 1
> Self-IPI: 9 18
> Normal IPI: 176 343
> Broadcast IPI: 0 9885
>
> CC: Andrew Morton <akpm@...ux-foundation.org>
> CC: Ashish Kalra <Ashish.Kalra@...ium.com>
> CC: Christoffer Dall <christoffer.dall@...aro.org>
> CC: Geert Uytterhoeven <geert@...ux-m68k.org>
> CC: Linu Cherian <Linu.Cherian@...ium.com>
> CC: Sunil Goutham <Sunil.Goutham@...ium.com>
> Signed-off-by: Yury Norov <ynorov@...iumnetworks.com>
> ---
> arch/Kconfig | 10 ++++
> kernel/Makefile | 1 +
> kernel/ipi_benchmark.c | 134 +++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 145 insertions(+)
> create mode 100644 kernel/ipi_benchmark.c
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 057370a0ac4e..80d6ef439199 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -82,6 +82,16 @@ config JUMP_LABEL
> ( On 32-bit x86, the necessary options added to the compiler
> flags may increase the size of the kernel slightly. )
>
> +config IPI_BENCHMARK
> + tristate "Test IPI performance on SMP systems"
> + depends on SMP
> + help
> + Test IPI performance on SMP systems. If system has only one online
> + CPU, sending IPI to other CPU is obviously not possible, and ENOENT
> + is returned for corresponding test.
> +
> + If unsure, say N.
> +
> config STATIC_KEYS_SELFTEST
> bool "Static key selftest"
> depends on JUMP_LABEL
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 172d151d429c..04e550e1990c 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -101,6 +101,7 @@ obj-$(CONFIG_TRACEPOINTS) += trace/
> obj-$(CONFIG_IRQ_WORK) += irq_work.o
> obj-$(CONFIG_CPU_PM) += cpu_pm.o
> obj-$(CONFIG_BPF) += bpf/
> +obj-$(CONFIG_IPI_BENCHMARK) += ipi_benchmark.o
>
> obj-$(CONFIG_PERF_EVENTS) += events/
>
> diff --git a/kernel/ipi_benchmark.c b/kernel/ipi_benchmark.c
> new file mode 100644
> index 000000000000..35f1f7598c36
> --- /dev/null
> +++ b/kernel/ipi_benchmark.c
> @@ -0,0 +1,134 @@
> +/*
> + * Performance test for IPI on SMP machines.
> + *
> + * Copyright (c) 2017 Cavium Networks.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of version 2 of the GNU General Public
> + * License as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + * General Public License for more details.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/ktime.h>
> +
> +#define NTIMES 100000
> +
> +#define POKE_ANY 0
> +#define DRY_RUN 1
> +#define POKE_SELF 2
> +#define POKE_ALL 3
> +
> +static void __init handle_ipi(void *t)
> +{
> + ktime_t *time = (ktime_t *) t;
> +
> + if (time)
> + *time = ktime_get() - *time;
> +}
> +
> +static ktime_t __init send_ipi(int flags)
> +{
> + ktime_t time;
> + unsigned int cpu = get_cpu();
> +
> + switch (flags) {
> + case POKE_ALL:
> + /* If broadcasting, don't force all CPUs to update time. */
> + smp_call_function_many(cpu_online_mask, handle_ipi, NULL, 1);
> + /* Fall thru */
> + case DRY_RUN:
> + /* Do everything except actually sending IPI. */
> + time = 0;
> + break;
> + case POKE_ANY:
> + cpu = cpumask_any_but(cpu_online_mask, cpu);
> + if (cpu >= nr_cpu_ids) {
> + time = -ENOENT;
> + break;
> + }
> + /* Fall thru */
> + case POKE_SELF:
> + time = ktime_get();
> + smp_call_function_single(cpu, handle_ipi, &time, 1);
> + break;
> + default:
> + time = -EINVAL;
> + }
> +
> + put_cpu();
> + return time;
> +}
> +
> +static int __init __bench_ipi(unsigned long i, ktime_t *time, int flags)
> +{
> + ktime_t t;
> +
> + *time = 0;
> + while (i--) {
> + t = send_ipi(flags);
> + if ((int) t < 0)
> + return (int) t;
> +
> + *time += t;
> + }
> +
> + return 0;
> +}
> +
> +static int __init bench_ipi(unsigned long times, int flags,
> + ktime_t *ipi, ktime_t *total)
> +{
> + int ret;
> +
> + *total = ktime_get();
> + ret = __bench_ipi(times, ipi, flags);
> + if (unlikely(ret))
> + return ret;
> +
> + *total = ktime_get() - *total;
> +
> + return 0;
> +}
> +
> +static int __init init_bench_ipi(void)
> +{
> + ktime_t ipi, total;
> + int ret;
> +
> + ret = bench_ipi(NTIMES, DRY_RUN, &ipi, &total);
> + if (ret)
> + pr_err("Dry-run FAILED: %d\n", ret);
> + else
> + pr_err("Dry-run: %18llu, %18llu ns\n", ipi, total);
you do not use NTIMES here to calculate the average value. Is that intended?
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