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Date: Tue, 23 Aug 2016 16:08:42 -0500 From: Josh Poimboeuf <jpoimboe@...hat.com> To: Andy Lutomirski <luto@...nel.org> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Frederic Weisbecker <fweisbec@...il.com>, Thomas Gleixner <tglx@...utronix.de>, Kees Cook <keescook@...omium.org>, "H . Peter Anvin" <hpa@...or.com>, Nilay Vaish <nilayvaish@...il.com>, the arch/x86 maintainers <x86@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Brian Gerst <brgerst@...il.com>, Byungchul Park <byungchul.park@....com>, Peter Zijlstra <peterz@...radead.org> Subject: Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder On Tue, Aug 23, 2016 at 01:31:20PM -0700, Andy Lutomirski wrote: > On Aug 23, 2016 12:11 AM, "Linus Torvalds" > So the fact that this seems to have any significant effect on > performance suggests to me that it's being run unnecessarily Yeah, I think check_object_size() is being run unnecessarily in a lot of cases. Calling it only when size is non-const would probably speed things up a lot. > or that somehow we're walking all the way to the top of the stack in > cases where we shouldn't have done so. I know that's not happening because this code would print a warning. > Josh, can you see an example call site in a profile of your test to > find out what this code is doing? I can try to figure it out tomorrow. But really it doesn't surprise me much that this patch makes arch_within_stack_frames() an order of magnitude slower. The original code was very simple, whereas __unwind_start() and unwind_next_frame() have a lot more code. -- Josh
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