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Date: Sun, 29 Oct 2017 13:21:21 -0700 From: Alexei Starovoitov <ast@...com> To: Sebastian Andrzej Siewior <bigeasy@...utronix.de> CC: <tglx@...utronix.de>, <peterz@...radead.org>, Daniel Borkmann <daniel@...earbox.net>, <netdev@...r.kernel.org> Subject: Re: [RFC] please clarify local_irq_disable() in pcpu_freelist_populate() On 10/29/17 1:14 PM, Sebastian Andrzej Siewior wrote: > On 2017-10-27 19:18:40 [-0700], Alexei Starovoitov wrote: >> pcpu_freelist_push() is called by bpf programs from atomic context. > > so raw would still be correct because the content is locked. it would be incorrect because this_* versions have good checks in them and no need to avoid them. >> lockdep thinks that __pcpu_freelist_push() can be called recursively >> in the middle of pcpu_freelist_populate's loop and will deadlock >> which is not the case here. That's why local_irq_save() is there. >> Just to silence lockdep. > > do you mind giving me bunch of test-cases so I can test it myself? samples/bpf/map_perf_test* >> While developing pcpu_freelist I've benchmarked many different >> approaches. Some of the numbers are in >> commit 6c9059817432 ("bpf: pre-allocate hash map elements") >> iirc I passed on llist, since llist_del_first still needs a lock, >> so doesn't really help. > > Okay. I will look that up. > > Sebastian >
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