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Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_E
From: |
Vijay Kilari |
Subject: |
Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register |
Date: |
Thu, 18 Aug 2016 13:26:07 +0530 |
On Wed, Aug 17, 2016 at 7:09 PM, Paolo Bonzini <address@hidden> wrote:
>
>
> On 16/08/2016 14:02, address@hidden wrote:
>> From: Vijaya Kumar K <address@hidden>
>>
>> Add helper API to read MIDR_EL1 registers to fetch
>> cpu identification information. This helps in
>> adding errata's and architecture specific features.
>>
>> This is implemented only for arm architecture.
>>
>> Signed-off-by: Vijaya Kumar K <address@hidden>
>> ---
>> include/qemu/aarch64-cpuid.h | 9 +++++
>> util/Makefile.objs | 1 +
>> util/aarch64-cpuid.c | 94
>> ++++++++++++++++++++++++++++++++++++++++++++
>> 3 files changed, 104 insertions(+)
>>
>> diff --git a/include/qemu/aarch64-cpuid.h b/include/qemu/aarch64-cpuid.h
>> new file mode 100644
>> index 0000000..3c11057
>> --- /dev/null
>> +++ b/include/qemu/aarch64-cpuid.h
>> @@ -0,0 +1,9 @@
>> +#ifndef QEMU_AARCH64_CPUID_H
>> +#define QEMU_AARCH64_CPUID_H
>> +
>> +#if defined (__aarch64__)
>> +uint64_t get_aarch64_cpu_id(void);
>> +bool is_thunderx_pass2_cpu(void);
>> +#endif
>> +
>> +#endif
>> diff --git a/util/Makefile.objs b/util/Makefile.objs
>> index 96cb1e0..aa07bc3 100644
>> --- a/util/Makefile.objs
>> +++ b/util/Makefile.objs
>> @@ -35,3 +35,4 @@ util-obj-y += log.o
>> util-obj-y += qdist.o
>> util-obj-y += qht.o
>> util-obj-y += range.o
>> +util-obj-y += aarch64-cpuid.o
>> diff --git a/util/aarch64-cpuid.c b/util/aarch64-cpuid.c
>> new file mode 100644
>> index 0000000..42af704
>> --- /dev/null
>> +++ b/util/aarch64-cpuid.c
>> @@ -0,0 +1,94 @@
>> +/*
>> + * Dealing with arm cpu identification information.
>> + *
>> + * Copyright (C) 2016 Cavium, Inc.
>> + *
>> + * Authors:
>> + * Vijaya Kumar K <address@hidden>
>> + *
>> + * This work is licensed under the terms of the GNU LGPL, version 2.1
>> + * or later. See the COPYING.LIB file in the top-level directory.
>> + */
>> +
>> +#include "qemu/osdep.h"
>> +#include "qemu-common.h"
>> +#include "qemu/cutils.h"
>> +#include "qemu/aarch64-cpuid.h"
>> +
>> +#if defined (__aarch64__)
>> +#define MIDR_IMPLEMENTER_SHIFT 24
>> +#define MIDR_IMPLEMENTER_MASK (0xffULL << MIDR_IMPLEMENTER_SHIFT)
>> +#define MIDR_ARCHITECTURE_SHIFT 16
>> +#define MIDR_ARCHITECTURE_MASK (0xf << MIDR_ARCHITECTURE_SHIFT)
>> +#define MIDR_PARTNUM_SHIFT 4
>> +#define MIDR_PARTNUM_MASK (0xfff << MIDR_PARTNUM_SHIFT)
>> +
>> +#define MIDR_CPU_PART(imp, partnum) \
>> + (((imp) << MIDR_IMPLEMENTER_SHIFT) | \
>> + (0xf << MIDR_ARCHITECTURE_SHIFT) | \
>> + ((partnum) << MIDR_PARTNUM_SHIFT))
>> +
>> +#define ARM_CPU_IMP_CAVIUM 0x43
>> +#define CAVIUM_CPU_PART_THUNDERX 0x0A1
>> +
>> +#define MIDR_THUNDERX_PASS2 \
>> + MIDR_CPU_PART(ARM_CPU_IMP_CAVIUM, CAVIUM_CPU_PART_THUNDERX)
>> +#define CPU_MODEL_MASK (MIDR_IMPLEMENTER_MASK | MIDR_ARCHITECTURE_MASK | \
>> + MIDR_PARTNUM_MASK)
>> +
>> +static uint64_t qemu_read_aarch64_midr_el1(void)
>> +{
>> +#ifdef CONFIG_LINUX
>> + const char *file =
>> "/sys/devices/system/cpu/cpu0/regs/identification/midr_el1";
>> + char *buf;
>> + uint64_t midr = 0;
>> +
>> +#define BUF_SIZE 32
>> + buf = g_malloc0(BUF_SIZE);
>> + if (!buf) {
>> + return 0;
>> + }
>> +
>> + if (!g_file_get_contents(file, &buf, 0, NULL)) {
>> + goto out;
>> + }
>> +
>> + if (qemu_strtoull(buf, NULL, 0, &midr) < 0) {
>> + goto out;
>> + }
>> +
>> +out:
>> + g_free(buf);
>> +
>> + return midr;
>> +#else
>> + return 0;
>> +#endif
>> +}
>> +
>> +static bool is_thunderx_cpu;
>> +static uint64_t aarch64_midr_val;
>> +uint64_t get_aarch64_cpu_id(void)
>> +{
>> +#ifdef CONFIG_LINUX
>> + static bool cpu_info_read;
>> +
>> + if (unlikely(!cpu_info_read)) {
>> + aarch64_midr_val = qemu_read_aarch64_midr_el1();
>> + aarch64_midr_val &= CPU_MODEL_MASK;
>> + cpu_info_read = 1;
>> + if (aarch64_midr_val == MIDR_THUNDERX_PASS2) {
>> + is_thunderx_cpu = 1;
>> + }
>> + }
>> + return aarch64_midr_val;
>> +#else
>> + return 0;
>> +#endif
>> +}
>> +
>> +bool is_thunderx_pass2_cpu(void)
>> +{
>> + return is_thunderx_cpu;
>
> This can be:
>
> return get_aarch64_cpu_id() == MIDR_THUNDERX_PASS2;
>
> without the is_thunderx_cpu variable.
The get_aarch_cpu_id() has check " if (unlikely(!cpu_info_read)) ".
If we call get_aarch_cpu_id() from is_thunderx_pass2_cpu() which is
called from inside the loop, we will be adding one additional check.
What I observed is having extra check inside the loop is adding 100 to
200ms overhead
on live migration time. So I added this variable extra is_thunderx_cpu
static variable
to make it simple single check.
>
> Paolo
>
>> +}
>> +#endif
>>
- [Qemu-devel] [RFC PATCH v2 0/2] Live migration optimization for Thunderx platform, vijay . kilari, 2016/08/16
- [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, vijay . kilari, 2016/08/16
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Paolo Bonzini, 2016/08/17
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register,
Vijay Kilari <=
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Paolo Bonzini, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Vijay Kilari, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Paolo Bonzini, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Richard Henderson, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Peter Maydell, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Richard Henderson, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Peter Maydell, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Vijay Kilari, 2016/08/19
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Richard Henderson, 2016/08/19
[Qemu-devel] [RFC PATCH v2 2/2] utils: Add prefetch for Thunderx platform, vijay . kilari, 2016/08/16