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From: | wangyanan (Y) |
Subject: | Re: [PATCH v5 02/14] hw/core/machine: Introduce CPU cluster topology support |
Date: | Wed, 29 Dec 2021 11:48:10 +0800 |
User-agent: | Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 |
Hi Philippe, Thanks for your review. On 2021/12/29 3:17, Philippe Mathieu-Daudé wrote:
Hi, On 12/28/21 10:22, Yanan Wang wrote:The new Cluster-Aware Scheduling support has landed in Linux 5.16, which has been proved to benefit the scheduling performance (e.g. load balance and wake_affine strategy) on both x86_64 and AArch64. So now in Linux 5.16 we have four-level arch-neutral CPU topology definition like below and a new scheduler level for clusters. struct cpu_topology { int thread_id; int core_id; int cluster_id; int package_id; int llc_id; cpumask_t thread_sibling; cpumask_t core_sibling; cpumask_t cluster_sibling; cpumask_t llc_sibling; } A cluster generally means a group of CPU cores which share L2 cache or other mid-level resources, and it is the shared resources that is used to improve scheduler's behavior. From the point of view of the size range, it's between CPU die and CPU core. For example, on some ARM64 Kunpeng servers, we have 6 clusters in each NUMA node, and 4 CPU cores in each cluster. The 4 CPU cores share a separate L2 cache and a L3 cache tag, which brings cache affinity advantage. In virtualization, on the Hosts which have pClusters, if we canMaybe [*] -> reference to pClusters?
Hm, I'm not sure what kind of reference is appropriate here. The third paragraph in the commit message has explained what a cluster generally means. We can also read the description of clusters in Linux kernel Kconfig files: [1] and [2]. [1]arm64: https://github.com/torvalds/linux/blob/master/arch/arm64/Kconfig config SCHED_CLUSTER bool "Cluster scheduler support" help Cluster scheduler support improves the CPU scheduler's decision making when dealing with machines that have clusters of CPUs. Cluster usually means a couple of CPUs which are placed closely by sharing mid-level caches, last-level cache tags or internal busses. [2]x86: https://github.com/torvalds/linux/blob/master/arch/x86/Kconfig config SCHED_CLUSTER bool "Cluster scheduler support" depends on SMP default y help Cluster scheduler support improves the CPU scheduler's decision making when dealing with machines that have clusters of CPUs. Cluster usually means a couple of CPUs which are placed closely by sharing mid-level caches, last-level cache tags or internal busses.
design a vCPU topology with cluster level for guest kernel and have a dedicated vCPU pinning. A Cluster-Aware Guest kernel can also make use of the cache affinity of CPU clusters to gain similar scheduling performance. This patch adds infrastructure for CPU cluster level topology configuration and parsing, so that the user can specify cluster parameter if their machines support it. Signed-off-by: Yanan Wang <wangyanan55@huawei.com> --- hw/core/machine-smp.c | 26 +++++++++++++++++++------- hw/core/machine.c | 3 +++ include/hw/boards.h | 6 +++++- qapi/machine.json | 5 ++++- qemu-options.hx | 7 ++++--- softmmu/vl.c | 3 +++ 6 files changed, 38 insertions(+), 12 deletions(-) diff --git a/qapi/machine.json b/qapi/machine.json index edeab6084b..ff0ab4ca20 100644 --- a/qapi/machine.json +++ b/qapi/machine.json @@ -1404,7 +1404,9 @@ # # @dies: number of dies per socket in the CPU topology # -# @cores: number of cores per die in the CPU topology +# @clusters: number of clusters per die in the CPU topologyMissing: # (since 7.0)
Ah, yes.
+# +# @cores: number of cores per cluster in the CPU topology # # @threads: number of threads per core in the CPU topology # @@ -1416,6 +1418,7 @@ '*cpus': 'int', '*sockets': 'int', '*dies': 'int', + '*clusters': 'int', '*cores': 'int', '*threads': 'int', '*maxcpus': 'int' } }If you want I can update the doc when applying.
Do you mean the missing "since 7.0"? If you have a plan to apply the first 1-7 patches separately and I don't need to respin, please help to update it, thank you! :) Thanks, Yanan
Thanks, Phil. .
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