On Fri, Jul 12, 2013 at 10:27:56AM +0200, Ingo Molnar wrote: > > * Robin Holt <holt@xxxxxxx> wrote: > > > [...] > > > > With this patch, we did boot a 16TiB machine. Without the patches, the > > v3.10 kernel with the same configuration took 407 seconds for > > free_all_bootmem. With the patches and operating on 2MiB pages instead > > of 1GiB, it took 26 seconds so performance was improved. I have no feel > > for how the 1GiB chunk size will perform. > > That's pretty impressive. > > It's still a 15x speedup instead of a 512x speedup, so I'd say there's > something else being the current bottleneck, besides page init > granularity. > > Can you boot with just a few gigs of RAM and stuff the rest into hotplug > memory, and then hot-add that memory? That would allow easy profiling of > remaining overhead. > > Side note: > > Robert Richter and Boris Petkov are working on 'persistent events' support > for perf, which will eventually allow boot time profiling - I'm not sure > if the patches and the tooling support is ready enough yet for your > purposes. > > Robert, Boris, the following workflow would be pretty intuitive: > > - kernel developer sets boot flag: perf=boot,freq=1khz,size=16MB > > - we'd get a single (cycles?) event running once the perf subsystem is up > and running, with a sampling frequency of 1 KHz, sending profiling > trace events to a sufficiently sized profiling buffer of 16 MB per > CPU. > > - once the system reaches SYSTEM_RUNNING, profiling is stopped either > automatically - or the user stops it via a new tooling command. > > - the profiling buffer is extracted into a regular perf.data via a > special 'perf record' call or some other, new perf tooling > solution/variant. > > [ Alternatively the kernel could attempt to construct a 'virtual' > perf.data from the persistent buffer, available via /sys/debug or > elsewhere in /sys - just like the kernel constructs a 'virtual' > /proc/kcore, etc. That file could be copied or used directly. ] Hello, Robert, Boris, Ingo. How about executing a perf in usermodehelper and collecting output in tmpfs? Using this approach, we can start a perf after rootfs initialization, because we need a perf binary at least. But we can use almost functionality of perf. If anyone have interest with this approach, I will send patches implementing this idea. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>