Borislav Petkov <[email protected]> writes: > On Tue, Sep 05, 2017 at 04:30:09PM +0300, Alexander Shishkin wrote: >> Detached events: a new flag to the perf syscall makes a 'detached' event, >> which exists after its file descriptor is released. Not all detached events >> are per-thread AUX events: this tries to take into account the need for >> system-wide persistent events too. > > Nice, thanks!
Forgot to mention that I did hack the tracepoint support into the tooling as well to make sure it's a workable idea. >> (2) Need to be able to kill those events, so they need to be accessible >> after they are created. >> Event files: detached events exist as files in tracefs (at the moment), can >> be opened/mmaped/read/removed. > > I guess I'll see when I continue reading but I remember us doing ioctls > on the event fd. Iirc that was for re-attaching to the event to make it 'normal' before closing. >> (6) Ring buffer memory accounting needs to take this new arrangement into >> account: one user can use up at most NR_CPUS * buffer_size memory at any >> given point in time. >> Only account the first such event and undo the accounting when the last >> event is gone. > > ... and I guess we probably shouldn't allow the user to create too many > events and shoot herself in the OOM-foot. Well, they are still limited by the RLIMIT_MEMLOCK and perf_event_mlock sysctl for the total amount of memory that can be pinned for the ring buffers at any given time, so that should be fine. >> (7) We'll also need to supply all the things that the [PT] decoder normally >> finds out via sysfs attributes, like clock ratios, capabilities, etc so that >> it also finds its way into the core dump file. >> "PMU info" structure is appended to the user page. >> >> I've also hack the perf tool to support all this, all these things can be >> found at [1]. I'm not posting the tooling patches though, them being >> thoroughly ugly and proof-of-concept. In short, perf record will create >> detached events with '--detached' and afterwards will open detached events >> via their path in tracefs. > > Sounds nice. I'd need to test all that just so I can be able to create > detached RAS events (which are tracepoints) with it. Thanks, let me know how it goes. Regards, -- Alex
