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0089-target-i386-present-virtual-L3-cach.patch
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File 0089-target-i386-present-virtual-L3-cach.patch of Package qemu.7456
From cc6d31453a4a0bf319147e0ad871cf2d665f446f Mon Sep 17 00:00:00 2001 From: Alexander Graf <agraf@suse.de> Date: Mon, 31 Oct 2016 17:19:44 +0100 Subject: [PATCH] target-i386: present virtual L3 cache info for vcpus Some software algorithms are based on the hardware's cache info, for example, for x86 linux kernel, when cpu1 want to wakeup a task on cpu2, cpu1 will trigger a resched IPI and told cpu2 to do the wakeup if they don't share low level cache. Oppositely, cpu1 will access cpu2's runqueue directly if they share llc. The relevant linux-kernel code as bellow: static void ttwu_queue(struct task_struct *p, int cpu) { struct rq *rq = cpu_rq(cpu); ...... if (... && !cpus_share_cache(smp_processor_id(), cpu)) { ...... ttwu_queue_remote(p, cpu); /* will trigger RES IPI */ return; } ...... ttwu_do_activate(rq, p, 0); /* access target's rq directly */ ...... } In real hardware, the cpus on the same socket share L3 cache, so one won't trigger a resched IPIs when wakeup a task on others. But QEMU doesn't present a virtual L3 cache info for VM, then the linux guest will trigger lots of RES IPIs under some workloads even if the virtual cpus belongs to the same virtual socket. For KVM, there will be lots of vmexit due to guest send IPIs. The workload is a SAP HANA's testsuite, we run it one round(about 40 minuates) and observe the (Suse11sp3)Guest's amounts of RES IPIs which triggering during the period: No-L3 With-L3(applied this patch) cpu0: 363890 44582 cpu1: 373405 43109 cpu2: 340783 43797 cpu3: 333854 43409 cpu4: 327170 40038 cpu5: 325491 39922 cpu6: 319129 42391 cpu7: 306480 41035 cpu8: 161139 32188 cpu9: 164649 31024 cpu10: 149823 30398 cpu11: 149823 32455 cpu12: 164830 35143 cpu13: 172269 35805 cpu14: 179979 33898 cpu15: 194505 32754 avg: 268963.6 40129.8 The VM's topology is "1*socket 8*cores 2*threads". After present virtual L3 cache info for VM, the amounts of RES IPIs in guest reduce 85%. For KVM, vcpus send IPIs will cause vmexit which is expensive, so it can cause severe performance degradation. We had tested the overall system performance if vcpus actually run on sparate physical socket. With L3 cache, the performance improves 7.2%~33.1%(avg:15.7%). Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> [agraf: cherry picked from 14c985cffa6cb177fc01a163d8bcf227c104718c] [agraf: disabled by default] Signed-off-by: Alexander Graf <agraf@suse.de> Conflicts: include/hw/i386/pc.h target-i386/cpu.c target-i386/cpu.h Conflicts: target-i386/cpu-qom.h target-i386/cpu.c --- target-i386/cpu-qom.h | 6 ++++++ target-i386/cpu.c | 49 ++++++++++++++++++++++++++++++++++++++++++++----- 2 files changed, 50 insertions(+), 5 deletions(-) diff --git a/target-i386/cpu-qom.h b/target-i386/cpu-qom.h index b0b13b1f11..1afe31ed1e 100644 --- a/target-i386/cpu-qom.h +++ b/target-i386/cpu-qom.h @@ -118,6 +118,12 @@ typedef struct X86CPU { /* Compatibility bits for old machine types: */ bool enable_cpuid_0xb; + /* Compatibility bits for old machine types. + * If true present virtual l3 cache for VM, the vcpus in the same virtual + * socket share an virtual l3 cache. + */ + bool enable_l3_cache; + /* in order to simplify APIC support, we leave this pointer to the user */ struct DeviceState *apic_state; diff --git a/target-i386/cpu.c b/target-i386/cpu.c index ac475143f9..dfe1552a97 100644 --- a/target-i386/cpu.c +++ b/target-i386/cpu.c @@ -56,6 +56,7 @@ #define CPUID_2_L1D_32KB_8WAY_64B 0x2c #define CPUID_2_L1I_32KB_8WAY_64B 0x30 #define CPUID_2_L2_2MB_8WAY_64B 0x7d +#define CPUID_2_L3_16MB_16WAY_64B 0x4d /* CPUID Leaf 4 constants: */ @@ -130,11 +131,18 @@ #define L2_LINES_PER_TAG 1 #define L2_SIZE_KB_AMD 512 -/* No L3 cache: */ +/* Level 3 unified cache: */ #define L3_SIZE_KB 0 /* disabled */ #define L3_ASSOCIATIVITY 0 /* disabled */ #define L3_LINES_PER_TAG 0 /* disabled */ #define L3_LINE_SIZE 0 /* disabled */ +#define L3_N_LINE_SIZE 64 +#define L3_N_ASSOCIATIVITY 16 +#define L3_N_SETS 16384 +#define L3_N_PARTITIONS 1 +#define L3_N_DESCRIPTOR CPUID_2_L3_16MB_16WAY_64B +#define L3_N_LINES_PER_TAG 1 +#define L3_N_SIZE_KB_AMD 16384 /* TLB definitions: */ @@ -2294,6 +2302,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, { X86CPU *cpu = x86_env_get_cpu(env); CPUState *cs = CPU(cpu); + uint32_t pkg_offset; /* test if maximum index reached */ if (index & 0x80000000) { @@ -2347,7 +2356,11 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, } *eax = 1; /* Number of CPUID[EAX=2] calls required */ *ebx = 0; - *ecx = 0; + if (!cpu->enable_l3_cache) { + *ecx = 0; + } else { + *ecx = L3_N_DESCRIPTOR; + } *edx = (L1D_DESCRIPTOR << 16) | \ (L1I_DESCRIPTOR << 8) | \ (L2_DESCRIPTOR); @@ -2393,6 +2406,25 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, *ecx = L2_SETS - 1; *edx = CPUID_4_NO_INVD_SHARING; break; + case 3: /* L3 cache info */ + if (!cpu->enable_l3_cache) { + *eax = 0; + *ebx = 0; + *ecx = 0; + *edx = 0; + break; + } + *eax |= CPUID_4_TYPE_UNIFIED | \ + CPUID_4_LEVEL(3) | \ + CPUID_4_SELF_INIT_LEVEL; + pkg_offset = apicid_pkg_offset(cs->nr_cores, cs->nr_threads); + *eax |= ((1 << pkg_offset) - 1) << 14; + *ebx = (L3_N_LINE_SIZE - 1) | \ + ((L3_N_PARTITIONS - 1) << 12) | \ + ((L3_N_ASSOCIATIVITY - 1) << 22); + *ecx = L3_N_SETS - 1; + *edx = CPUID_4_INCLUSIVE | CPUID_4_COMPLEX_IDX; + break; default: /* end of info */ *eax = 0; *ebx = 0; @@ -2604,9 +2636,15 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, *ecx = (L2_SIZE_KB_AMD << 16) | \ (AMD_ENC_ASSOC(L2_ASSOCIATIVITY) << 12) | \ (L2_LINES_PER_TAG << 8) | (L2_LINE_SIZE); - *edx = ((L3_SIZE_KB/512) << 18) | \ - (AMD_ENC_ASSOC(L3_ASSOCIATIVITY) << 12) | \ - (L3_LINES_PER_TAG << 8) | (L3_LINE_SIZE); + if (!cpu->enable_l3_cache) { + *edx = ((L3_SIZE_KB / 512) << 18) | \ + (AMD_ENC_ASSOC(L3_ASSOCIATIVITY) << 12) | \ + (L3_LINES_PER_TAG << 8) | (L3_LINE_SIZE); + } else { + *edx = ((L3_N_SIZE_KB_AMD / 512) << 18) | \ + (AMD_ENC_ASSOC(L3_N_ASSOCIATIVITY) << 12) | \ + (L3_N_LINES_PER_TAG << 8) | (L3_N_LINE_SIZE); + } break; case 0x80000007: *eax = 0; @@ -3253,6 +3291,7 @@ static Property x86_cpu_properties[] = { DEFINE_PROP_UINT32("xlevel2", X86CPU, env.cpuid_xlevel2, 0), DEFINE_PROP_STRING("hv-vendor-id", X86CPU, hyperv_vendor_id), DEFINE_PROP_BOOL("cpuid-0xb", X86CPU, enable_cpuid_0xb, false), + DEFINE_PROP_BOOL("l3-cache", X86CPU, enable_l3_cache, false), DEFINE_PROP_END_OF_LIST() };
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