Messages in this thread | | | Subject | Re: [PATCH v4 09/16] perf tools: Enable indices setting syntax for BPF maps | From | pi3orama <> | Date | Fri, 11 Dec 2015 20:57:54 +0800 |
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发自我的 iPhone
> 在 2015年12月11日,下午8:47,Arnaldo Carvalho de Melo <acme@kernel.org> 写道: > > Em Fri, Dec 11, 2015 at 08:39:35PM +0800, pi3orama escreveu: >> >> >> 发自我的 iPhone >> >>> 在 2015年12月11日,下午8:15,Arnaldo Carvalho de Melo <acme@kernel.org> 写道: >>> >>> Em Fri, Dec 11, 2015 at 09:11:45AM -0300, Arnaldo Carvalho de Melo escreveu: >>>> Em Tue, Dec 08, 2015 at 02:25:37AM +0000, Wang Nan escreveu: >>>>> This patch introduce a new syntax to perf event parser: >>>>> >>>>> # perf record -e bpf_file.c/maps.mymap.value[0,3...5,7]=1234/ ... >>>> >>>> Is the above example valid? Wouldn't this be "maps:mymap.value" ? >>>> >>>>> >>>>> By utilizing the basic facilities in bpf-loader.c which allow setting >>>>> different slots in a BPF map separately, the newly introduced syntax >>>>> allows perf to control specific elements in a BPF map. >>>>> >>>>> Test result: >>>>> >>>>> # cat ./test_bpf_map_3.c >>>>> /************************ BEGIN **************************/ >>>>> #define SEC(NAME) __attribute__((section(NAME), used)) >>>>> enum bpf_map_type { >>>>> BPF_MAP_TYPE_ARRAY = 2, >>>>> }; >>>>> struct bpf_map_def { >>>>> unsigned int type; >>>>> unsigned int key_size; >>>>> unsigned int value_size; >>>>> unsigned int max_entries; >>>>> }; >>>>> static void *(*map_lookup_elem)(struct bpf_map_def *, void *) = >>>>> (void *)1; >>>>> static int (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) = >>>>> (void *)6; >>>> >>>> Can you explain the above a bit more? What are the magic 1 and 6 values? >>> >>> So, from another patch: >>> >>> static u64 (*bpf_ktime_get_ns)(void) = >>> (void *)5; >>> static int (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) = >>> (void *)6; >>> static int (*bpf_get_smp_processor_id)(void) = >>> (void *)8; >>> static int (*bpf_perf_event_output)(void *, struct bpf_map_def *, int, >>> void *, unsigned long) = >>> (void *)23; >>> >>> Where can I get this magical mistery table? Could this be hidden away in >>> some .h file automagically included in bpf scriptlets so that n00bies >>> like me don't have to be wtf'ing? >> >> They are function numbers defined in bpf.h and bpf-common.h, but they are Linux >> headers. Directly include them causes many error for llvm. Also, the function >> prototypes are BPF specific and can't included in Linux source. We should have >> a place holds those indices and prototypes together. > > Sure, just please don't assume whoever is reading your patches has this > background, provide comments above such places, so that reviewing gets > facilitated. > > I eventually figured this is some sort of trampoline to access kernel > functions: > > /* integer value in 'imm' field of BPF_CALL instruction selects which > * helper function eBPF program intends to call > */ > enum bpf_func_id { > BPF_FUNC_unspec, > BPF_FUNC_map_lookup_elem, /* void *map_lookup_elem(&map, &key) */ > BPF_FUNC_map_update_elem, /* int map_update_elem(&map, &key, &value, flags) */ > BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */ > BPF_FUNC_probe_read, /* int bpf_probe_read(void *dst, int size, void *src) */ > > > But if you had just: > > /* > * See enum_bpf_func_id in ./include/uapi/linux/bpf.h > */ > > That would've helped. >
Thank you, but I think this is a good chance to setup the policy about the header files for BPF. I suggested to put BPF specific headers into Linux kernel include dir, but we must find a way to avoid Linux includes them. Another useful structure is pt_regs, however which is not as important as before because we have prologue now.
I'd like to have a try next week.
Thank you.
> - Arnaldo
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