(2014/02/28 7:22), Masami Hiramatsu wrote: > (2014/02/28 6:45), Andi Kleen wrote: >> Masami Hiramatsu <masami.hiramatsu...@hitachi.com> writes: >> >>> Currently, since the kprobes expects to be used >>> with less than 100 probe points, its hash table >>> just has 64 entries. This is too little to handle >>> several thousands of probes. >>> Enlarge this to 4096 entires which just consumes >>> 32KB (on 64bit arch) for better scalability. >> >> 32K for a debug feature that most systems never use seems >> too large to me. >> >> First can you check if smaller hash tables work too >> (perhaps with a better hash, like jhash) > > I doubt jhash helps it, but yes, at least the various size > should be tested.
Here, I tested the hash table performance with 2^6 to 2^12. Cycles% of get_kprobe with 10k probes: Size Cycles% 2^6 95.58% 2^7 85.83% 2^8 68.43% 2^9 48.61% 2^10 46.95% 2^11 48.46% 2^12 56.95% So, we can see the hash table larger than 2^9 (512 entries, which consumes 4KB) has no performance improvement. Would you think 4kB is still big for kprobes? :) Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology 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/
