(2014/04/24 18:01), Ingo Molnar wrote: > > * Masami Hiramatsu <masami.hiramatsu...@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.
Thanks :) > > So I don't think this should be a Kconfig entry, just enable it > unconditionally. That will further simplify the code. Hmm, it consumes some amount of memory (36KB/core) just for the case of several thousand of kprobes. On enterprise servers and desktop it's OK, no problem. But I think, some embedded systems with small resources will not want that. So, how about enabling Kconfig by default? Thank you, -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
