Hi, On 2/15/2023 10:42 AM, Alexei Starovoitov wrote: > On Tue, Feb 14, 2023 at 6:36 PM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote: >> Hi, >> >> On 2/12/2023 12:33 AM, Alexei Starovoitov wrote: >>> On Fri, Feb 10, 2023 at 5:10 PM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote: >>>>>> Hou, are you plannning to resubmit this change? I also hit this while testing my >>>>>> changes on bpf-next. >>>>> Are you talking about the whole patch set or just GFP_ZERO in mem_alloc? >>>>> The former will take a long time to settle. >>>>> The latter is trivial. >>>>> To unblock yourself just add GFP_ZERO in an extra patch? >>>> Sorry for the long delay. Just find find out time to do some tests to compare >>>> the performance of bzero and ctor. After it is done, will resubmit on next week. >>> I still don't like ctor as a concept. In general the callbacks in the critical >>> path are guaranteed to be slow due to retpoline overhead. >>> Please send a patch to add GFP_ZERO. >> I see. Will do. But i think it is better to know the coarse overhead of these >> two methods, so I hack map_perf_test to support customizable value size for >> hash_map_alloc and do some benchmarks to show the overheads of ctor and >> GFP_ZERO. These benchmark are conducted on a KVM-VM with 8-cpus, it seems when >> the number of allocated elements is small, the overheads of ctor and bzero are >> basically the same, but when the number of allocated element increases (e.g., >> half full), the overhead of ctor will be bigger. For big value size, the >> overhead of ctor and zero are basically the same, and it seems due to the main >> overhead comes from slab allocation. The following is the detailed results: > and with retpoline? Yes. Forge to mention that. The following is the output of vulnerabilities directory: # cd /sys/devices/system/cpu/vulnerabilities # grep . * itlb_multihit:Processor vulnerable l1tf:Mitigation: PTE Inversion mds:Vulnerable: Clear CPU buffers attempted, no microcode; SMT Host state unknown meltdown:Mitigation: PTI mmio_stale_data:Unknown: No mitigations retbleed:Not affected spec_store_bypass:Vulnerable spectre_v1:Mitigation: usercopy/swapgs barriers and __user pointer sanitization spectre_v2:Mitigation: Retpolines, STIBP: disabled, RSB filling, PBRSB-eIBRS: Not affected srbds:Not affected tsx_async_abort:Not affected
