On Fri, Dec 6, 2013 at 3:54 PM, Masami Hiramatsu <masami.hiramatsu...@hitachi.com> wrote: > (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. :)
it is indeed very cool. Thanks! -- 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/
