| Date | Thu, 24 Apr 2014 11:01:34 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH -tip v9 25/26] kprobes: Introduce kprobe cache to reduce cache misshits |
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* Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:
> Introduce kprobe cache to reduce cache misshits for > massive multiple kprobes. > For stress testing kprobes, we need to activate kprobes > as many as possible. This situation causes cache miss > hit storm on kprobe hash-list. kprobe hashlist is already > enlarged to 4k entries and this is still small for 40k > kprobes. > > For example, when registering 40k probes on the hlist and > enabling 20k probes, perf tools shows still a lot of > cache-misses are on the get_kprobe. > ---- > Samples: 633 of event 'cache-misses', Event count (approx.): 3414776 > + 68.13% [k] get_kprobe > + 4.38% [k] ftrace_lookup_ip > + 2.54% [k] kprobe_ftrace_handler > ---- > > Also, I found that the most of the kprobes are not hit. > In that case, to reduce cache-misses, we can reduce the > random memory access by introducing a per-cpu cache which > caches the address of frequently used kprobe data structure > and its probe address. > > With kpcache enabled, the get_kprobe_cached goes down to > around 4-5% of cache-misses with 20k probes. > ---- > Samples: 729 of event 'cache-misses', Event count (approx.): 690125 > + 14.49% [k] ftrace_lookup_ip > + 5.61% [k] kprobe_trace_func > + 5.17% [k] kprobe_ftrace_handler > + 4.62% [k] get_kprobe_cached > ---- > > Of course this reduces the enabling time too. > > Without this fix (just enlarge hash table): > (2934 sec, 1 min intervals for each 2000 probes enabled) > > ---- > Enabling trace events: start at 1393921862 > 0 1393921864 a2mp_chan_alloc_skb_cb_38581 > ... > 19999 1393924928 nfs4_open_confirm_done_11785 > ---- > > With this fix: > (2025 sec, 1 min intervals for each 2000 probes enabled)
That's a nice speedup.
So I don't think this should be a Kconfig entry, just enable it unconditionally. That will further simplify the code.
Thanks,
Ingo
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