Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [ltt-dev] LTTng 0.87 improved page fault tracing | Date | Thu, 29 Jan 2009 13:47:05 +0900 (JST) |
| |
> * KOSAKI Motohiro (kosaki.motohiro@jp.fujitsu.com) wrote: > > Hi > > > > interesting.. > > > > > I just combined the 4 page fault handler events that were in the tracing > > > hot path of LTTng into 2 : > > > > > > kernel page_fault_entry > > > kernel page_fault_exit > > > > > > They take as parameter the combination of what was available in the > > > trap_entry/exit events and handle_mm_fault entry/exit events. This > > > should lessen the performance impact of the tracer when it's active. > > > I did the related modifications in LTTV 0.12.8. > > > > Just question. > > > > As far as I know, customer has two different requeremtn of the page fault. > > 1 a) > > (1) collect number of all page fault > > -> if it is too large, too many interrupt decrease performance. > (a single event is required for this) > > 1 b) the user may also want to know the time spent in the page fault > handler to service those faults, therefore involving page fault > entry and exit events.
Indeed. that's great.
> > (2) collect number of major page fault > > -> major page fault indicate to increase random access I/O, > > then, some customer want to collect major page fault > > (don't include minor page fault) > > Yes, the trace_page_fault_exit takes the "fault" parameter returned by > handle_mm_fault (which is recorded to the trace as the "res" event > field). Using > > res & VM_FAULT_MAJOR > > will give only the major page faults. Note that some knowledge of the > bitmask is required to interpret the "res" bitfield. This could be done > by a specific analysis module. I would ideally like to create a LTTng > module to export tables including those bitfields so we can keep the > bitfield interpretation in sync with the kernel code changes more or > less automatically.
Agreed. thanks for great improvement.
> > > > > Is this patch fill (2) requirement? > > > > Yes. > > Mathieu > > > > > > > -- > Mathieu Desnoyers > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
| |