Messages in this thread | | | Date | Tue, 22 Aug 2023 11:51:30 +0800 | Subject | Re: [RFC] KVM: arm/arm64: optimize vSGI injection performance | From | zhaoxu <> |
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hi marc, thanks for reviewing.
On 2023/8/21 18:16, Marc Zyngier wrote: >>> This work is based on v5.4, and here is test data: > > This is a 4 year old kernel. I'm afraid you'll have to provide > something that is relevant to a current (e.i. v6.5) kernel. > In fact, the core vCPU search algorithm remains the same in the latest kernel: iterate all vCPUs, if mpidr matches, inject. next version will based on latest kernel.
>>> Based on the test results, the performance of vm with less than 16 cores remains almost the same, >>> while significant improvement can be observed with more than 16 >>> cores. > > This triggers multiple questions: > > - what is the test being used? on what hardware? how can I reproduce > this data? > 1. I utilized the ipi_benchmark (https://patchwork.kernel.org/project/linux-arm-kernel/patch/20171211141600.24401-1-ynorov@caviumnetworks.com/) with a modification to the Normal IPI target in the following manner: smp_call_function_single(31, handle_ipi, &time, 1). 2. On kunpeng 920 platform. 3. Using ipi_benchmark but change the target cpu in Normal IPI case, and use bcc or bpftrace to measuret the execution time of vgic_v3_dispatch_sgi. > - which current guest OS *currently* make use of broadcast or 1:N > SGIs? Linux doesn't and overall SGI multicasting is pretty useless > to an OS. > > [...] Yes, arm64 linux almost never send broadcast ipi. I will use another test data to prove performence improvement > >>> /* >>> - * Compare a given affinity (level 1-3 and a level 0 mask, from the SGI >>> - * generation register ICC_SGI1R_EL1) with a given VCPU. >>> - * If the VCPU's MPIDR matches, return the level0 affinity, otherwise >>> - * return -1. >>> + * Get affinity routing index from ICC_SGI_* register >>> + * format: >>> + * aff3 aff2 aff1 aff0 >>> + * |- 8 bits -|- 8 bits -|- 8 bits -|- 4 bits or 8bits -| > > OK, so you are implementing RSS support: > > - Why isn't that mentioned anywhere in the commit log? > > - Given that KVM actively limits the MPIDR to 4 bits at Aff0, how does > it even work the first place? > > - How is that advertised to the guest? > > - How can the guest enable RSS support? > thanks to mention that, I also checked the relevant code, guest can't enable RSS, it was my oversight. This part has removed in next version. > This is not following the GICv3 architecture, and I'm sceptical that > it actually works as is (I strongly suspect that you have additional > patches...). there are nothing left, all the patchs are here > > M. > With regards Xu
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