From: Mel Gorman <mgorman@suse.de>
To: Jiri Slaby <jslaby@suse.cz>
Cc: Ingo Molnar <mingo@kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
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>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH 00/10] x86: undwarf unwinder
Date: Fri, 2 Jun 2017 11:40:48 +0100 [thread overview]
Message-ID: <20170602104048.jkkzssljsompjdwy@suse.de> (raw)
In-Reply-To: <3db1be2a-cc33-89f3-950f-cfe1c21ee7f1@suse.cz>
On Thu, Jun 01, 2017 at 04:08:25PM +0200, Jiri Slaby wrote:
> Ccing Mel who did proper measurements and can hopefully comment on his
> results.
>
> On 06/01/2017, 03:50 PM, Ingo Molnar wrote:
> > That's not what I meant! The speedup comes from (hopefully) being able to disable
> > CONFIG_FRAME_POINTER, which:
> >
> > - creates simpler/faster function prologues and epilogues - no managing of RBP
> > needed
> >
> > - gives one more generic purpose register to work from. This matters less on
> > 64-bit kernels but it's a small effect.
> >
> > I've seen numbers of 1-2% of instruction count reduction in common kernel
> > workloads, which would be pretty significant on well cached workloads.
>
I didn't preserve the data involved but in a variety of workloads including
netperf, page allocator microbenchmark, pgbench and sqlite, enabling
framepointer introduced overhead of around the 5-10% mark. According
to an internal report I gave at the time, hackbench-thread-sockets was
around the 5% mark and a perf run showed "3.49% more cache misses with
framepointer enabled and 6.59% more cycles". Additional notes I made at
the time although again, without the original data is
---8<---
It looks like a small amount of overhead added everywhere and the size of
the vmlinux files supports that
text data bss dec hex filename
8143072 6480614 11153408 25777094 18953c6 vmlinux/decker/vmlinux-4.8.0-disable-fp
8396698 6480614 11153408 26030720 18d3280 vmlinux/decker/vmlinux-4.8.0-enable-fp
I also took a closer look at the pagealloc microbenchmarks because they
rely on so few functions. Profiles were not always captured due to the
short-lived nature of some of the tests so I looked at batches of 16384
allocation/frees of order-0 pages. Overall it showed 4.46% decline with
framepointer enabled and profiling. 3.89% more cycles and 24.94% more
cache misses.
As before, the framepointer cache miss overhead is not that obvious as
the bulk of samples take place elsewhere -- in this case, in checking
whether pages are buddies when merging. It's slightly clearer in
__rmqueue where 17.9% of cache misses are in the function entry point
with framepointer enabled vs 4.04% with framepointer disabled.
---8<---
Granted, the check was done back in 4.8, but I've no reason to believe
that 4.12 is any different and enabling framepointer does have a quite
substantial hit to workloads that spent a lot of time in the kernel.
--
Mel Gorman
SUSE Labs
prev parent reply other threads:[~2017-06-02 10:41 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-01 5:44 [RFC PATCH 00/10] x86: undwarf unwinder 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
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 [this message]
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