Messages in this thread | | | Date | Tue, 16 Dec 2008 23:38:51 +0100 | From | "Frédéric Weisbecker" <> | Subject | Re: [PATCH] tracing/ftrace: use preempt_enable_no_resched_notrace in ring_buffer_time_stamp() |
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2008/12/16 Ingo Molnar <mingo@elte.hu>: > > * Frédéric Weisbecker <fweisbec@gmail.com> wrote: > >> 2008/12/16 Ingo Molnar <mingo@elte.hu>: >> > >> > * Frederic Weisbecker <fweisbec@gmail.com> wrote: >> > >> >> Impact: prevent a trace recursion >> >> >> >> After some tests with function graph tracer under x86-32, I saw some recursions >> >> caused by ring_buffer_time_stamp() that calls preempt_enable_no_notrace() which >> >> calls preempt_schedule() which is traced itself. >> >> >> >> This patch re-enables preemption without rescheduling. >> >> >> >> Cc: Steven Rostedt <rostedt@goodmis.org> >> >> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> >> >> --- >> >> kernel/trace/ring_buffer.c | 2 +- >> >> 1 files changed, 1 insertions(+), 1 deletions(-) >> > >> > applied to tip/tracing/ftrace, thanks Frederic! >> > >> > Does this explain+fix the weird crashes/reboots you were seeing? >> > >> > Ingo >> > >> >> No, actually the functions tracers are protected against recursion, >> but rescheduling attempts >> during all trace insertions (and moreover a call to >> prepare_ftrace_return with cancelled insertion) >> is a useless payload. >> >> The hard reboots I've seen are related to x86-64 while >> disabling/reenabling a CPU through /sys/device/system/cpu No tracer was >> enabled at these times (the problem still remains with latest updates on >> -tip for half an hour). >> >> One other thing: I've seen these pointless calls to preempt_schedule >> while testing the function graph tracer on VirtualBox. Since it provides >> virtual serial lines, it was more easy to debug than usual (I haven't >> any serial line on my box). The function graph tracer hangs on >> VirtualBox with a x86-32 -tip. It seems that the tracing is too slow and >> so hrtimer_interrupt() does an eternal loop, assuming that a new time >> update has to be done (because too much time elapsed during th tracing) >> after each iteration. I'm not sure what to do...disabling tracing for >> hrtimers or.... > > reduce HZ? > > Ingo >
I just switched from 250 to 100 HZ. And it remains the same. But I commented out the early_printk which could consume some time too. Perhaps there is one other thing that makes it hanging. I will investigate more... Did someone make some tests with function graph tracer on 32 bits these last days? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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