linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "H. Peter Anvin" <hpa@zytor.com>
To: Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Vince Weaver <vincent.weaver@maine.edu>,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@redhat.com>,
	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Subject: Re: perf_fuzzer compiled for x32 causes reboot
Date: Sat, 01 Mar 2014 08:50:17 -0800	[thread overview]
Message-ID: <7f55737e-25a2-4cf0-aa07-17102a368ef2@email.android.com> (raw)
In-Reply-To: <20140301095042.GA16524@pd.tnic>

The bottom line is that if we want hard numbers we probably have to measure.

Hoisting the cr2 read is a no-brainer, might even help performance...

On March 1, 2014 1:50:42 AM PST, Borislav Petkov <bp@alien8.de> wrote:
>On Sat, Mar 01, 2014 at 10:16:50AM +0100, Ingo Molnar wrote:
>> 
>> * Steven Rostedt <rostedt@goodmis.org> wrote:
>> 
>> > > Also, this function is called a _LOT_ under certain workloads, I 
>> > > don't know how cheap a CR2 read is, but it had better be really 
>> > > cheap.
>> > 
>> > That's a HPA question.
>> 
>> We read CR2 in the page fault hot path, so it's on the top of CPU 
>> architects' minds and it's reasonably optimized. A couple of cycles 
>> IIRC, but would be nice to hear actual numbers.
>
>Yeah, we were discussing this last night on IRC.
>
>And hpa actually meant that the optimization potential was there but no
>one did do it, except maybe Transmeta. :-)
>
>So the expensive thing is writing to CR2 because it is a serializing
>instruction. In fact, all writes to control registers except CR8 are
>serializing.
>
>The reading from CR2 should be cheaper but not as cheap as a normal
>MOV %reg %reg is. On AMD, MOV %reg, %cr2 is done with microcode so
>definitely at least a couple of cycles and I'd guess it is not a
>trivial
>MOV on Intel too.
>
>Maybe a way to hide this cost is the OoO, as hpa suggested, depending
>on
>how much parallelism that particular code region can offer (serializing
>instructions close by).

-- 
Sent from my mobile phone.  Please pardon brevity and lack of formatting.

  reply	other threads:[~2014-03-01 16:51 UTC|newest]

Thread overview: 115+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-02-21 20:25 perf_fuzzer causes reboot Vince Weaver
2014-02-21 22:13 ` perf_fuzzer compiled for x32 " Vince Weaver
2014-02-21 22:34   ` Vince Weaver
2014-02-22  4:50     ` Vince Weaver
2014-02-22  5:03       ` H. Peter Anvin
2014-02-22  6:26       ` H. Peter Anvin
2014-02-23  5:18         ` Vince Weaver
2014-02-23  5:24           ` H. Peter Anvin
2014-02-23  6:07           ` H. Peter Anvin
2014-02-23 14:05             ` Vince Weaver
2014-02-24  3:02               ` Vince Weaver
2014-02-24  5:22                 ` H. Peter Anvin
2014-02-24 15:35                   ` Vince Weaver
2014-02-24 16:34                     ` Vince Weaver
2014-02-24 16:47                       ` H. Peter Anvin
2014-02-24 17:10                         ` Vince Weaver
2014-02-24 17:25                           ` Peter Zijlstra
2014-02-24 17:32                             ` Vince Weaver
2014-02-24 17:40                               ` H. Peter Anvin
2014-02-24 18:00                                 ` Vince Weaver
2014-02-24 18:07                                   ` Vince Weaver
2014-02-24 18:34                                     ` H. Peter Anvin
2014-02-24 19:13                                       ` Steven Rostedt
2014-02-24 19:15                                         ` H. Peter Anvin
2014-02-24 19:30                                         ` Peter Zijlstra
2014-02-24 19:32                                           ` Steven Rostedt
2014-02-25  3:49                                           ` H. Peter Anvin
2014-02-25 14:07                                             ` Vince Weaver
2014-02-25 14:34                                               ` H. Peter Anvin
2014-02-25 14:43                                                 ` Steven Rostedt
2014-02-25 15:33                                                   ` Vince Weaver
2014-02-26 15:06                                                     ` Vince Weaver
2014-02-27 22:06                                                       ` Vince Weaver
2014-02-27 22:31                                                         ` Steven Rostedt
2014-02-27 22:52                                                           ` H. Peter Anvin
2014-02-27 23:30                                                             ` Steven Rostedt
2014-02-27 23:46                                                               ` H. Peter Anvin
2014-02-28  1:00                                                                 ` Vince Weaver
2014-02-28 20:34                                                                   ` Paul E. McKenney
2014-02-28 20:47                                                                     ` Steven Rostedt
2014-02-28 20:54                                                                       ` Peter Zijlstra
2014-02-28 21:17                                                                         ` Paul E. McKenney
2014-02-28 21:27                                                                           ` Peter Zijlstra
2014-02-28 21:51                                                                             ` Paul E. McKenney
2014-02-28 21:55                                                                               ` Peter Zijlstra
2014-02-28 22:05                                                                                 ` Steven Rostedt
2014-02-28 22:23                                                                                   ` Paul E. McKenney
2014-02-28  1:34                                                             ` Vince Weaver
2014-02-28  2:17                                                               ` H. Peter Anvin
2014-02-28  2:57                                                               ` Steven Rostedt
2014-02-28 11:11                                                                 ` Peter Zijlstra
2014-02-28 13:37                                                                   ` Steven Rostedt
2014-02-28 14:15                                                                 ` Vince Weaver
2014-02-28 14:23                                                                   ` Steven Rostedt
2014-02-28 15:07                                                                     ` Vince Weaver
2014-02-28 15:13                                                                       ` H. Peter Anvin
2014-02-28 15:40                                                                         ` Peter Zijlstra
2014-02-28 16:15                                                                           ` H. Peter Anvin
2014-02-28 16:29                                                                             ` Steven Rostedt
2014-02-28 19:33                                                                               ` [PATCH] x86: Rename copy_from_user_nmi() to copy_from_user_trace() Steven Rostedt
2014-02-28 20:46                                                                                 ` Peter Zijlstra
2014-02-28 20:51                                                                                   ` Steven Rostedt
2014-02-28 20:58                                                                                     ` Peter Zijlstra
2014-02-28 21:01                                                                                   ` Steven Rostedt
2014-02-28 21:17                                                                                     ` Peter Zijlstra
2014-02-28 20:56                                                                               ` perf_fuzzer compiled for x32 causes reboot Peter Zijlstra
2014-02-28 21:06                                                                                 ` Steven Rostedt
2014-03-01  9:16                                                                                   ` Ingo Molnar
2014-03-01  9:50                                                                                     ` Borislav Petkov
2014-03-01 16:50                                                                                       ` H. Peter Anvin [this message]
2014-03-04 23:05                                                                                         ` Borislav Petkov
2014-03-03  9:16                                                                                     ` Peter Zijlstra
2014-02-28 20:55                                                                             ` Peter Zijlstra
2014-02-28 15:20                                                                       ` Steven Rostedt
2014-02-28 15:30                                                                         ` Steven Rostedt
2014-02-28 20:38                                                                       ` H. Peter Anvin
2014-02-28 20:46                                                                         ` Steven Rostedt
2014-02-28 21:18                                                                         ` Vince Weaver
2014-02-28 21:30                                                                           ` Steven Rostedt
2014-02-28 23:34                                                                             ` Vince Weaver
2014-03-01  0:43                                                                               ` H. Peter Anvin
2014-03-01  3:36                                                                               ` Steven Rostedt
2014-03-01 16:24                                                                                 ` Andi Kleen
2014-03-02 15:34                                                                                   ` Vince Weaver
2014-03-02 16:02                                                                                 ` Vince Weaver
2014-02-28  9:39                                                           ` Peter Zijlstra
2014-02-24 17:40                               ` Peter Zijlstra
2014-02-24 17:41                               ` Vince Weaver
2014-02-24 17:42                                 ` H. Peter Anvin
2014-02-24 17:52                             ` H. Peter Anvin
2014-02-28 15:33 [PATCH] x86 trace: Fix page fault tracing bug Jiri Olsa
2014-02-28 15:47 ` Peter Zijlstra
2014-02-28 16:05   ` [PATCHv2] " Jiri Olsa
2014-02-28 16:11     ` H. Peter Anvin
2014-02-28 16:23       ` Steven Rostedt
2014-02-28 16:15     ` Steven Rostedt
2014-03-05  0:03     ` [tip:x86/urgent] x86, trace: Fix CR2 corruption when tracing page faults tip-bot for Jiri Olsa
2014-03-05 11:14       ` Peter Zijlstra
2014-03-05 12:20         ` Steven Rostedt
2014-03-05 12:25           ` Peter Zijlstra
2014-03-05 12:33             ` Steven Rostedt
2014-03-05 12:54               ` Peter Zijlstra
2014-03-05 13:02                 ` Peter Zijlstra
2014-03-05 13:07                   ` Peter Zijlstra
2014-03-05 12:36             ` Peter Zijlstra
2014-03-05 13:00               ` Steven Rostedt
2014-03-05 13:08                 ` Peter Zijlstra
2014-03-05 21:37                   ` H. Peter Anvin
2014-03-06  8:40                     ` Peter Zijlstra
2014-03-06 11:02                       ` Steven Rostedt
2014-03-06 14:53                         ` [PATCH] x86: Further robustify CR2 handling vs tracing Peter Zijlstra
2014-03-07 23:07                           ` [tip:x86/urgent] x86, trace: " tip-bot for Peter Zijlstra
2014-02-28 15:47 ` [PATCH] x86 trace: Fix page fault tracing bug Jiri Olsa
2014-02-28 16:00   ` Steven Rostedt
2014-02-28 16:01 ` Steven Rostedt

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=7f55737e-25a2-4cf0-aa07-17102a368ef2@email.android.com \
    --to=hpa@zytor.com \
    --cc=acme@ghostprotocols.net \
    --cc=bp@alien8.de \
    --cc=jolsa@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=vincent.weaver@maine.edu \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).