Messages in this thread | | | Date | Tue, 24 Nov 2009 16:04:15 +0800 | From | Li Zefan <> | Subject | Re: [PATCH 0/5] perf kmem: Add more functions and show more statistics |
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Ingo Molnar wrote: > * Pekka Enberg <penberg@cs.helsinki.fi> wrote: > >> Hi Li, >> >> On Tue, Nov 24, 2009 at 7:25 AM, Li Zefan <lizf@cn.fujitsu.com> wrote: >>> Pekka, do you think we can remove kmemtrace now? >> One more use case I forgot to mention: boot time tracing. Much of the >> persistent kernel memory footprint comes from the boot process which >> is why it's important to be able to trace memory allocations >> immediately after kmem_cache_init() has run. Can we make "perf kmem" >> do that? Eduard put most of his efforts into making that work for >> kmemtrace. > > Would be lovely if someone looked at perf from that angle (and extended > it). > > Another interesting area would be to allow a capture session without a > process context running immediately. (i.e. pre-allocate all the buffers, > use them, for a later 'perf save' to pick it up.) > > The two are kind of the same thing conceptually: a boot time trace is a > preallocated 'process context less' recording, to be picked up after > bootup. > > [ It also brings us 'stability/persistency of event logging' - i.e. a > capture session could be started and guaranteed by the kernel to be > underway, regardless of what user-space does. ] > > Btw., Arjan is doing a _lot_ of boot time tracing for Moblin, and he > indicated it in the past that starting a perf recording session from an > initrd is a pretty practical substitute as well. (I've Cc:-ed Arjan.) >
It would be great if perf can be used for boot time tracing. This needs pretty big work on kernel side.
>> On Tue, Nov 24, 2009 at 7:25 AM, Li Zefan <lizf@cn.fujitsu.com> wrote: >> >>> With kmem trace events, low-level analyzing can be done using >>> ftrace, and high-level analyzing can be done using perf-kmem. >>> >>> And chance is, more people may use and improve perf-kmem, and it >>> will be well-maintained within the perf infrastructure. On the other >>> hand, I guess few people use and contribute to kmemtrace-user. >> Sure, I think "perf kmem" is the way forward. I'd love to hear >> Eduard's comments on this before we remove the code from kernel. Do we >> need to do that for 2.6.33 or can we postpone that for 2.6.34? > > Certainly we can postpone it, as long as there's rough strategic > consensus on the way forward. I'd hate to have two overlapping core > kernel facilities and friction between the groups pursuing them and > constant distraction from having two targets. > > Such situations just rarely end with a good solution for the user - see > security modules for a horror story ... > > [ I dont think it will occur here, just wanted to mention it out of > abundance of caution that 1.5 decades of kernel hacking experience > inflicts on me ;-) ] >
Yeah, so we'd like to remove most of tracers, but I'm not rushing to remove kmemtrace for .33.
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