(2013/12/06 14:16), Alexei Starovoitov wrote: > On Thu, Dec 5, 2013 at 5:20 PM, Andi Kleen <a...@firstfloor.org> wrote: >>> the difference is bigger now: 484-145 vs 185-145 >> >> This is a obvious improvement, but imho not big enough to be extremely >> compelling (< cost 1-2 cache misses, no orders of magnitude improvements >> that would justify a lot of code) > > hmm. we're comparing against ktap here… > which has 5x more kernel code and 8x slower in this test... > >> Your code requires a compiler, so from my perspective it >> wouldn't be a lot easier or faster to use than just changing >> the code directly and recompile. >> >> The users want something simple too that shields them from >> having to learn all the internals. They don't want to recompile. >> As far as I can tell your code is a bit too low level for that, >> and the requirement for the compiler may also scare them. >> >> Where exactly does it fit? > > the goal is to have llvm compiler next to perf, wrapped in a user friendly > way. > > compiling small filter vs recompiling full kernel… > inserting into live kernel vs rebooting … > not sure how you're saying it's equivalent. > > In my kernel debugging experience current tools (tracing, systemtap) > were rarely enough. > I always had to add my own printks through the code, recompile and reboot. > Often just to see that it's not the place where I want to print things > or it's too verbose. > Then I would adjust printks, recompile and reboot again. > That was slow and tedious, since I would be crashing things from time to time > just because skb doesn't always have a valid dev or I made a typo. > For debugging I do really need something quick and dirty that lets me > add my own printk > of whatever structs I want anywhere in the kernel without crashing it. > That's exactly what bpf tracing filters do.
I recommend you to use perf-probe. That will give you an easy solution. :) 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/
