Yicong Yang <yangyicong@xxxxxxxxxx> writes: > From: Yicong Yang <yangyicong@xxxxxxxxxxxxx> > > Though ARM64 has the hardware to do tlb shootdown, the hardware > broadcasting is not free. > A simplest micro benchmark shows even on snapdragon 888 with only > 8 cores, the overhead for ptep_clear_flush is huge even for paging > out one page mapped by only one process: > 5.36% a.out [kernel.kallsyms] [k] ptep_clear_flush > > While pages are mapped by multiple processes or HW has more CPUs, > the cost should become even higher due to the bad scalability of > tlb shootdown. > > The same benchmark can result in 16.99% CPU consumption on ARM64 > server with around 100 cores according to Yicong's test on patch > 4/4. > > This patchset leverages the existing BATCHED_UNMAP_TLB_FLUSH by > 1. only send tlbi instructions in the first stage - > arch_tlbbatch_add_mm() > 2. wait for the completion of tlbi by dsb while doing tlbbatch > sync in arch_tlbbatch_flush() > Testing on snapdragon shows the overhead of ptep_clear_flush > is removed by the patchset. The micro benchmark becomes 5% faster > even for one page mapped by single process on snapdragon 888. > > With this support we're possible to do more optimization for memory > reclamation and migration[*]. I applied the patches on v6.1-rc4 and was able to see the drop in ptep_clear_flush() in the perf report when running the test program from Patch 2. The tests were done on a rk3399 based system with benefits visible when running the tests on either of the clusters. So, for the series, Tested-by: Punit Agrawal <punit.agrawal@xxxxxxxxxxxxx> Thanks, Punit [...]
