Messages in this thread | | | Date | Mon, 19 Dec 2011 18:04:47 +0100 | From | Oleg Nesterov <> | Subject | [PATCH RESEND 0/2] tracing: signal tracepoints |
| |
Steven, sorry for delay...
On 12/02, Steven Rostedt wrote: > > On Tue, 2011-11-22 at 21:52 +0100, Oleg Nesterov wrote: > > > > > Is "result" used for anything but tracepoints? When tracing is disabled, > > > the tracepoints should be just nops (when jump_label is enabled). Thus > > > tracing is very light. But if we are constantly calculating "result", > > > this is unused by those that don't use the tracing infrastructure, which > > > is 99.99% of all users. This is what I meant. > > > > Ah I see. I thought you dislike OVERFLOW_FAIL/LOSE_INFO namely. > > > > Of course, you are right. OTOH, this patch shaves 1058 bytes from > > .text. And without CONFIG_TRACE* gcc doesn't generate the extra code. > > I was just noting that when tracing is disabled (CONFIG_TRACE* is set, > like it is on distros, but tracing is not happening), that we have extra > code. We usually strive to have tracing configured into the kernel, but > produces no (actually as little as possible) overhead when not actively > tracing.
Yes, yes, I see. But I do not see any alternative. Of course, instead of adding "int result" we could add more trace_signal_generate's into the code, but imho this is too ugly. And in fact I am not sure this means less overhead with CONFIG_TRACE* even if this code is nop'ed.
> That said, you know this code much more than I do. If this isn't a fast > path, and spinning a few more CPU cycles and perhaps dirtying a few > cache lines floats your boat. I'm OK with this change.
I simply do not know. I _think_ that the overhead is negligible, the extra calculating just adds a couple of "mov CONSTANT, REGISTER" insns.
> > Oh. I simply do not know what can I do. Obviously, I'd like to avoid > > the new tracepoints in __send_signal(), imho this would be ugly. But > > the users want more info. > > > > OK. let me send the patch at least for review. May be someone will > > nack it authoritatively, in this case I can relax and forward the > > nack back to bugzilla ;) > > Again, if you don't think adding very slight overhead to this path is an > issue. Go ahead and add it.
OK, thanks.
The next question is, how can I add it ;) May be Ingo or Andrew could take these patches? Original signal tracepoints were routed via tip-tree...
Add them both to TO:, lets see who is kinder.
> > However, at least 2/2 looks very reasonable to me. In fact it looks > > almost like the bug-fix. > > 2/2 looks to have the extra overhead to. Is the bug fix just with the > trace point. > > Again, if you don't mind the overhead, then here: > > Acked-by: Steven Rostedt <rostedt@goodmis.org>
Thanks, included.
Oleg.
| |