From: Daniel Kiper <daniel.kiper@oracle.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Juergen Gross <JGross@suse.com>,
sstabellini@kernel.org, Andrew Cooper <andrew.cooper3@citrix.com>,
cardoe@cardoe.com, pgnet.dev@gmail.com, ning.sun@intel.com,
julien.grall@arm.com, david.vrabel@citrix.com,
xen-devel@lists.xenproject.org, qiaowei.ren@intel.com,
gang.wei@intel.com, fu.wei@linaro.org
Subject: Re: [PATCH v9 07/13] x86: add multiboot2 protocol support for EFI platforms
Date: Wed, 30 Nov 2016 18:21:25 +0100 [thread overview]
Message-ID: <20161130172125.GX18527@olila.local.net-space.pl> (raw)
In-Reply-To: <583EE96D0200007800123B98@prv-mh.provo.novell.com>
On Wed, Nov 30, 2016 at 06:59:57AM -0700, Jan Beulich wrote:
> >>> On 30.11.16 at 14:45, <daniel.kiper@oracle.com> wrote:
> > On Fri, Nov 25, 2016 at 12:50:55AM -0700, Jan Beulich wrote:
> >> >>> On 24.11.16 at 22:44, <daniel.kiper@oracle.com> wrote:
> >> > On Thu, Nov 24, 2016 at 04:08:12AM -0700, Jan Beulich wrote:
> >> >> >>> On 23.11.16 at 19:52, <andrew.cooper3@citrix.com> wrote:
> >> >> > Always use add/sub 1 in preference to inc and dec. They are the same
> >> >> > length to encode in 64bit, and avoids a pipeline stall from a merge of
> >> >> > the eflags register.
> >> >>
> >> >> What you say regarding length not true - add/sub need to encode
> >> >> the immediate somewhere (even if the operand was a register,
> >> >> inc/dec would still be smaller than add/sub, just not by as much as
> >> >> in 32-bit code). And the pipeline stall, afaik, affects only rather old
> >> >> processors.
> >> >
> >> > Intel 64 and IA-32 Architectures Optimization Reference Manual, section
> >> > 3.5.1.1, Use of the INC and DEC Instructions says nothing about exceptions.
> >>
> >> Which by itself is suspicious, as the dependency issue had been
> >> introduced only in (iirc) Pentium4. And anyway, this is a general
> >
> > Hmmm... Interesting... It looks that INC/DEC behavior has not changed since
> > the beginning (why it would change? It would not make sense).
>
> Please properly disambiguate "behavior": Architectural behavior of
> course can't change. Performance, otoh, has changed many times.
Right!
> And the resource dependency issue did appear only once the
> pipelining of instructions was sophisticated enough, but not good
> enough yet to track (as a dependency) EFLAGS.CF separately from
> the other arithmetic result flags.
OK, make sense right now. Thanks for explanation.
Daniel
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next prev parent reply other threads:[~2016-11-30 17:22 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-29 21:42 [PATCH v9 00/13] x86: multiboot2 protocol support Daniel Kiper
2016-09-29 21:42 ` [PATCH v9 01/13] x86: add " Daniel Kiper
2016-09-29 21:42 ` [PATCH v9 02/13] efi: create efi_enabled() Daniel Kiper
2016-09-29 21:42 ` [PATCH v9 03/13] x86: allow EFI reboot method neither on EFI platforms Daniel Kiper
2016-09-29 21:42 ` [PATCH v9 04/13] x86: properly calculate xen ELF end of image address Daniel Kiper
2016-09-30 9:43 ` Jan Beulich
2016-09-29 21:42 ` [PATCH v9 05/13] efi: build xen.gz with EFI code Daniel Kiper
2016-09-29 21:42 ` [PATCH v9 06/13] efi: create new early memory allocator Daniel Kiper
2016-09-30 9:46 ` Jan Beulich
2016-09-30 10:49 ` Daniel Kiper
2016-10-05 7:02 ` Daniel Kiper
2016-10-05 15:45 ` Julien Grall
2016-10-05 18:30 ` Julien Grall
2016-10-06 12:21 ` Jan Beulich
2016-10-11 13:39 ` Julien Grall
2016-10-12 11:45 ` Jan Beulich
2016-10-12 12:51 ` Julien Grall
2016-10-12 12:59 ` Jan Beulich
2016-10-24 9:03 ` Daniel Kiper
2016-10-24 9:57 ` Jan Beulich
2016-11-03 13:48 ` Daniel Kiper
2016-11-10 10:34 ` Daniel Kiper
2016-10-31 13:32 ` Julien Grall
2016-09-29 21:42 ` [PATCH v9 07/13] x86: add multiboot2 protocol support for EFI platforms Daniel Kiper
2016-11-23 18:52 ` Andrew Cooper
2016-11-24 11:08 ` Jan Beulich
2016-11-24 21:44 ` Daniel Kiper
2016-11-25 7:50 ` Jan Beulich
2016-11-30 13:45 ` Daniel Kiper
2016-11-30 13:59 ` Jan Beulich
2016-11-30 17:21 ` Daniel Kiper [this message]
2016-11-24 21:31 ` Daniel Kiper
2016-09-29 21:42 ` [PATCH v9 08/13] x86/boot: implement early command line parser in C Daniel Kiper
2016-09-29 21:42 ` [PATCH v9 09/13] x86: change default load address from 1 MiB to 2 MiB Daniel Kiper
2016-09-30 10:02 ` Jan Beulich
2016-09-29 21:42 ` [PATCH v9 10/13] x86/setup: use XEN_IMG_OFFSET instead of Daniel Kiper
2016-09-29 21:42 ` [PATCH v9 11/13] x86: make Xen early boot code relocatable Daniel Kiper
2016-09-29 21:42 ` [PATCH v9 12/13] x86/boot: rename sym_phys() to sym_offs() Daniel Kiper
2016-09-29 21:42 ` [PATCH v9 13/13] x86: add multiboot2 protocol support for relocatable images Daniel Kiper
2016-09-30 10:03 ` Jan Beulich
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