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From: Jiri Slaby <jslaby@suse.cz>
To: Peter Zijlstra <peterz@infradead.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	live-patching@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [RFC PATCH 00/10] x86: undwarf unwinder
Date: Thu, 1 Jun 2017 14:33:20 +0200
Message-ID: <d2ca5435-6386-29b8-db87-7f227c2b713a@suse.cz> (raw)
In-Reply-To: <20170601121721.lezoecnyah3aic6a@hirez.programming.kicks-ass.net>

On 06/01/2017, 02:17 PM, Peter Zijlstra wrote:
> On Thu, Jun 01, 2017 at 06:58:20AM -0500, Josh Poimboeuf wrote:
>>> Being able to generate more optimal code in the hottest code paths of the kernel 
>>> is the _real_, primary upstream kernel benefit of a different debuginfo method - 
>>> which has to be weighed against the pain of introducing a new unwinder. But this 
>>> submission does not talk about that aspect at all, which should be fixed I think.
>>
>> Actually I devoted an entire one-sentence paragraph to performance in
>> the documentation:
>>
>>   The simpler debuginfo format also enables the unwinder to be relatively
>>   fast, which is important for perf and lockdep.
>>
>> But I'll try to highlight that a little more.
> 
> That's relative to a DWARF unwinder. It doesn't appear to be possible to
> get anywhere near a frame-pointer unwinder due to having to do this
> log(n) lookup for every single frame.

This is ~ 20 times faster than my DWARF unwinder by a quick measurement
(20000 calls to save_stack_trace via single vfs_write).

perf profile, if you care:

__save_stack_trace
|
|--65.89%--unwind_next_frame
|          |
|          |--53.64%--__undwarf_lookup
|          |
|           --5.30%--deref_stack_reg
|                     |
|                      --2.32%--stack_access_ok
|
|--24.17%--__unwind_start
|          |
|          |--21.52%--unwind_next_frame
|          |          |
|          |          |--14.24%--__undwarf_lookup
|          |          |
|          |           --2.98%--deref_stack_reg
|          |                     |
|          |                      --1.32%--stack_access_ok
|          |
|           --1.32%--get_stack_info
|                     |
|                      --0.66%--in_task_stack
|
|--3.31%--unwind_get_return_address
|          __kernel_text_address
|          |
|          |--0.99%--is_ftrace_trampoline
|          |
|          |--0.99%--__is_insn_slot_addr
|          |          |
|          |           --0.66%--__rcu_read_unlock
|          |
|           --0.66%--is_bpf_text_address
|
 --1.66%--save_stack_address


-- 
js
suse labs

  reply index

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-01  5:44 Josh Poimboeuf
2017-06-01  5:44 ` [RFC PATCH 01/10] objtool: move checking code to check.c Josh Poimboeuf
2017-06-14  7:22   ` Jiri Slaby
2017-06-01  5:44 ` [RFC PATCH 02/10] objtool, x86: add several functions and files to the objtool whitelist Josh Poimboeuf
2017-06-14  7:24   ` Jiri Slaby
2017-06-14 13:03     ` Josh Poimboeuf
2017-06-01  5:44 ` [RFC PATCH 03/10] objtool: stack validation 2.0 Josh Poimboeuf
2017-06-01  5:44 ` [RFC PATCH 04/10] objtool: add undwarf debuginfo generation Josh Poimboeuf
2017-06-14  8:42   ` Jiri Slaby
2017-06-14 13:27     ` Josh Poimboeuf
2017-06-22  7:47       ` Jiri Slaby
2017-06-22 12:49         ` Josh Poimboeuf
2017-06-01  5:44 ` [RFC PATCH 05/10] objtool, x86: add facility for asm code to provide CFI hints Josh Poimboeuf
2017-06-01 13:57   ` Andy Lutomirski
2017-06-01 14:16     ` Josh Poimboeuf
2017-06-01 14:40       ` Andy Lutomirski
2017-06-01 15:02         ` Josh Poimboeuf
2017-06-01  5:44 ` [RFC PATCH 06/10] x86/entry: add CFI hint undwarf annotations Josh Poimboeuf
2017-06-01 14:03   ` Andy Lutomirski
2017-06-01 14:23     ` Josh Poimboeuf
2017-06-01 14:28       ` Josh Poimboeuf
2017-06-01 14:39         ` Andy Lutomirski
2017-06-01 15:01           ` Josh Poimboeuf
2017-06-01  5:44 ` [RFC PATCH 07/10] x86/asm: add CFI hint annotations to sync_core() Josh Poimboeuf
2017-06-01  5:44 ` [RFC PATCH 08/10] extable: rename 'sortextable' script to 'sorttable' Josh Poimboeuf
2017-06-01  5:44 ` [RFC PATCH 09/10] extable: add undwarf table sorting ability to sorttable script Josh Poimboeuf
2017-06-01  5:44 ` [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Josh Poimboeuf
2017-06-01 11:05   ` Peter Zijlstra
2017-06-01 12:26     ` Josh Poimboeuf
2017-06-01 12:47       ` Jiri Slaby
2017-06-01 13:02         ` Josh Poimboeuf
2017-06-01 13:42         ` Peter Zijlstra
2017-06-01 13:10       ` Peter Zijlstra
2017-06-01 12:13   ` Peter Zijlstra
2017-06-01 12:36     ` Josh Poimboeuf
2017-06-01 13:12       ` Peter Zijlstra
2017-06-01 15:03         ` Josh Poimboeuf
2017-06-14 11:45   ` Jiri Slaby
2017-06-14 13:44     ` Josh Poimboeuf
2017-06-01  6:08 ` [RFC PATCH 00/10] x86: " Ingo Molnar
2017-06-01 11:58   ` Josh Poimboeuf
2017-06-01 12:17     ` Peter Zijlstra
2017-06-01 12:33       ` Jiri Slaby [this message]
2017-06-01 12:52         ` Josh Poimboeuf
2017-06-01 12:57           ` Jiri Slaby
2017-06-01 12:47       ` Josh Poimboeuf
2017-06-01 13:25         ` Peter Zijlstra
2017-06-06 14:14           ` Sergey Senozhatsky
2017-06-01 13:50         ` Andy Lutomirski
2017-06-01 13:50     ` Ingo Molnar
2017-06-01 13:58       ` Jiri Slaby
2017-06-02  8:30         ` Jiri Slaby
2017-06-01 14:05       ` Josh Poimboeuf
2017-06-01 14:08       ` Jiri Slaby
2017-06-02 10:40         ` Mel Gorman

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