Messages in this thread | | | Subject | Re: [PATCH bpf] bpf: Do not grab the bucket spinlock by default on htab batch ops | From | Daniel Borkmann <> | Date | Tue, 18 Feb 2020 16:56:24 +0100 |
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On 2/18/20 4:43 PM, Yonghong Song wrote: > On 2/14/20 2:43 PM, Brian Vazquez wrote: >> Grabbing the spinlock for every bucket even if it's empty, was causing >> significant perfomance cost when traversing htab maps that have only a >> few entries. This patch addresses the issue by checking first the >> bucket_cnt, if the bucket has some entries then we go and grab the >> spinlock and proceed with the batching. >> >> Tested with a htab of size 50K and different value of populated entries. >> >> Before: >> Benchmark Time(ns) CPU(ns) >> --------------------------------------------- >> BM_DumpHashMap/1 2759655 2752033 >> BM_DumpHashMap/10 2933722 2930825 >> BM_DumpHashMap/200 3171680 3170265 >> BM_DumpHashMap/500 3639607 3635511 >> BM_DumpHashMap/1000 4369008 4364981 >> BM_DumpHashMap/5k 11171919 11134028 >> BM_DumpHashMap/20k 69150080 69033496 >> BM_DumpHashMap/39k 190501036 190226162 >> >> After: >> Benchmark Time(ns) CPU(ns) >> --------------------------------------------- >> BM_DumpHashMap/1 202707 200109 >> BM_DumpHashMap/10 213441 210569 >> BM_DumpHashMap/200 478641 472350 >> BM_DumpHashMap/500 980061 967102 >> BM_DumpHashMap/1000 1863835 1839575 >> BM_DumpHashMap/5k 8961836 8902540 >> BM_DumpHashMap/20k 69761497 69322756 >> BM_DumpHashMap/39k 187437830 186551111 >> >> Fixes: 057996380a42 ("bpf: Add batch ops to all htab bpf map") >> Cc: Yonghong Song <yhs@fb.com> >> Signed-off-by: Brian Vazquez <brianvv@google.com> > > Acked-by: Yonghong Song <yhs@fb.com>
I must probably be missing something, but how is this safe? Presume we traverse in the walk with bucket_cnt = 0. Meanwhile a different CPU added entries to this bucket since not locked. Same reader on the other CPU with bucket_cnt = 0 then starts to traverse the second hlist_nulls_for_each_entry_safe() unlocked e.g. deleting entries?
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