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Date: Tue, 14 Jan 2014 19:51:34 -0500 From: Steven Rostedt <rostedt@...dmis.org> To: Petr Mladek <pmladek@...e.cz> Cc: Frederic Weisbecker <fweisbec@...il.com>, Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org, x86@...nel.org Subject: Re: [PATCH v6 5/8] x86: do not trace __probe_kernel_read On Tue, 10 Dec 2013 16:42:17 +0100 Petr Mladek <pmladek@...e.cz> wrote: > probe_kernel_read is used when modifying function calls in ftrace_replace_code, > see arch/x86/kernel/ftrace.c. On x86, the code is replaced using int3 guard. > All functions are patched in parallel to reduce an expensive synchronization > of all CPUs. The result is that all affected functions are called via > ftrace_int3_handler during the process. > > ftrace_int3_handler is relatively slow because it has to check whether > it is responsible for the handled IP. Therefore we should not modify > functions that used during patching. It would slowdown the patching. > > I tried to switch between 7 tracers: blk, branch, function_graph, wakeup_rt, > irqsoff, function, and nop. Every tracer has also been enabled and disabled. > With 500 cycles, I got these times before this commit: > > real 18m2.477s 18m8.654s 18m9.196s > user 0m0.008s 0m0.008s 0m0.012s > sys 0m17.316s 0m17.104s 0m17.300s > > and after this commit: > > real 16m14.390s 16m15.200s 16m19.632s > user 0m0.028s 0m0.024s 0m0.028s > sys 0m23.788s 0m23.812s 0m23.804s > Actually no. The benefit of tracing a function outweighs the benefit of speeding up the conversion. If you want a fast conversion, simply: echo __probe_kernel_read > /sys/kernel/debug/tracing/set_ftrace_notrace Try your numbers again with the above line. -- Steve > Signed-off-by: Petr Mladek <pmladek@...e.cz> > --- > mm/maccess.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/maccess.c b/mm/maccess.c > index d53adf9ba84b..bed9ee854ea0 100644 > --- a/mm/maccess.c > +++ b/mm/maccess.c > @@ -18,7 +18,7 @@ > long __weak probe_kernel_read(void *dst, const void *src, size_t size) > __attribute__((alias("__probe_kernel_read"))); > > -long __probe_kernel_read(void *dst, const void *src, size_t size) > +long notrace __probe_kernel_read(void *dst, const void *src, size_t size) > { > long ret; > mm_segment_t old_fs = get_fs(); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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