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@xxxxxxxxxxxxxxxxxx/)
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
