(2014/11/05 0:51), Pawel Moll wrote: > On Tue, 2014-11-04 at 09:24 +0000, Masami Hiramatsu wrote: >> What I'd like to do is the binary version of ftrace-marker, the text >> version is already supported by qemu (see below). >> https://lists.gnu.org/archive/html/qemu-devel/2013-04/msg00505.html >> >> But since that is just a string data (not structured data), it is hard to >> analyze via perf-script or some other useful filters/triggers in ftrace. >> >> In my idea, the new event will be defined via a special file in debugfs like >> kprobe-events, like below. >> >> # cd $debugfs/tracing >> # echo "newgrp/newevent signarg:s32 flag:u64" >> marker_events >> # cat events/newgrp/newevent/format >> name: newevent >> ID: 2048 >> format: >> field:unsigned short common_type; offset:0; size:2; signed:0; >> field:unsigned char common_flags; offset:2; size:1; signed:0; >> field:unsigned char common_preempt_count; offset:3; size:1;signed:0; >> field:int common_pid; offset:4; size:4; signed:1; >> >> field:s32 signarg; offset:8; size:4; signed:1; >> field:u64 flag; offset:12; size:8; signed:0; >> >> print fmt: "signarg=%d flag=0x%Lx", REC->signarg, REC->flag >> >> Then, users will write the data (excluded common fields) when the event happens >> via trace_marker which start with '\0'ID(in u32). Kernel just checks the ID and >> its data size, but doesn't parse, filter/trigger it and log it into the kernel buffer. > > Very neat, I like it! Certainly useful with scripting. Any gut feeling > regarding the kernel version it will be ready for? 3.19 or later than > that? Thanks, and not yet implemented, I'd like to ask people about the format etc. before that :) >> Of course, this has a downside that the user must have a privilege to access to debugfs. >> Thus maybe we need both of prctl() IF for perf and this IF for ftrace. > > I don't have any particularly strong feelings about the solution as long > as I'm able to create this "synchronisation point" of mine in the perf > data. In one of this patch's previous incarnations I was also doing a > write() to the perf fd to achieve pretty much the same result. > > In my personal use case root access to debugfs isn't a problem (I need > it for other ftrace operations anyway). However Ingo and some other guys > seemed interested in prctl() approach because: 1. it's much simpler to > use even comparing with simple trace_marker's open(path)/write()/close() > and 2. because any process can do it at any time and the results are > quietly discarded if no one is listening. I also remember that when I > proposed sort of "unification" between trace_marker and the uevents, > Ingo straight away "suggested" keeping it separate. Agreed, I think we can keep trace_marker opened (so application will just need to write() the events), but for the second reason, prctl will be better for per-application usage. Actually, ftrace is "system-wide" oriented, but the perf is not. Thank you, -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@xxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
