On Mon, Feb 11, 2013 at 05:16:34PM +0100, Jan Kara wrote: > > postmark-2917 [000] .... 196.435786: jbd2_handle_stats: dev 254,32 > > tid 570 type 2 line_no 2541 interval 311 sync 0 requested_blocks 1 > > dirtied_blocks 0 > Nice! I'm just wondering - won't it be easier if we just stored a pointer > to __FILE__ in the handle? We wouldn't have to define those transaction > types and think which one to use when coding. Also checking the trace point > output would be simpler. I guess using __FILE__ will increase kernel size > due to additional string constants as gcc isn't clever enough to merge > identical strings. But we could workaround that defining in every ext4 > file: One of the reasons why I originally started with using an integer type was that I was originally thinking about calculating handle-level statistics (max hold time, average hold time, etc., and keeping those statistics on a per-class basis). So having an integer type number was useful for that purpose. Once I figured out that you could do things specify constraints such as "interval > 5", the desire to do kernel-level statistics became less urgent for me, since it's really finding the "long pole" handle hold times which are most interesting. I still might want to some kernel-level statistics which are broken down by type, since once we eliminate the long pole, knowing what the average handle hold times are could still be useful/interesting. Another downside of using a pointer to __FILE__, or some static character pointer, is that it doesn't work for the applications such as perf (and I think ftrace, although I'm not certain about the ftrace tool, since I never use it) can't handle printing the char *, since they use the ring buffer syscall directly instead of using the TP_printk statement. So all they get is a kernel address, and something which is useful to decode. But for users who are using the /sys/kernel/debug/tracing interface via echo and cat, I do agree that using a static char *JBD_FILE so that /sys/kernel/debug/trace has real file names would be a bit more convenient for them. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
