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From: "H. Peter Anvin" <hpa@zytor.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: mjg59@srcf.ucam.org, jkosina@suse.cz, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org, ebiederm@xmission.com,
	greg@kroah.com
Subject: Re: [PATCH 07/11] kexec: Create a relocatable object called purgatory
Date: Tue, 25 Feb 2014 08:55:42 -0800	[thread overview]
Message-ID: <530CCB0E.3060009@zytor.com> (raw)
In-Reply-To: <20140225164342.GC2701@redhat.com>

On 02/25/2014 08:43 AM, Vivek Goyal wrote:
> 
> W.r.t sharing the code with arch/x86/boot/, I am not sure how to do it.
> 

Pretty much we have been doing #includes (a bit sad, I know)... there
are already a lot of them between arch/x86/boot,
arch/x86/boot/compressed, and arch/x86/realmode.  In that sense
collecting these "limited environments" together and have these kinds of
stuff together in one place seems like a good idea.

Does purgatory move large amounts of data around?  If so, we probably
*do* want to use rep movsl, but otherwise you're definitely right, using
C code makes more sense.

> I see two implementations of memcpy() under arch/x86/boot.
> 
> One is in copy.S. This is assembly code and looks like is supposed to
> run in 16bit mode. (code16).
> 
> Other one is in compressed/misc.c and there are two definitions, one
> for 32bit and one fore 64bit.

They are basically the 16-, 32-, and 64-bit variants of the same code.

> I am not sure why there is a need to write memcpy() in assembly when
> C will do just fine for my case. I don't have to write two versions of
> memcpy() and use it both for 32bit and 64bit.

The point would be to use the ones we already have.

> So I can just make all the purgatory code share same version of memcpy(),
> memcmp() and memset(), is that fine. I have taken implementations of
> these functions from lib/string.c

It depends on if you care about performance.  For memcpy() and memset()
in particular, the CPU has internally optimized versions of these that
beats C at least on any newer silicon.

	-hpa


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WARNING: multiple messages have this Message-ID (diff)
From: "H. Peter Anvin" <hpa@zytor.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
	ebiederm@xmission.com, mjg59@srcf.ucam.org, greg@kroah.com,
	jkosina@suse.cz
Subject: Re: [PATCH 07/11] kexec: Create a relocatable object called purgatory
Date: Tue, 25 Feb 2014 08:55:42 -0800	[thread overview]
Message-ID: <530CCB0E.3060009@zytor.com> (raw)
In-Reply-To: <20140225164342.GC2701@redhat.com>

On 02/25/2014 08:43 AM, Vivek Goyal wrote:
> 
> W.r.t sharing the code with arch/x86/boot/, I am not sure how to do it.
> 

Pretty much we have been doing #includes (a bit sad, I know)... there
are already a lot of them between arch/x86/boot,
arch/x86/boot/compressed, and arch/x86/realmode.  In that sense
collecting these "limited environments" together and have these kinds of
stuff together in one place seems like a good idea.

Does purgatory move large amounts of data around?  If so, we probably
*do* want to use rep movsl, but otherwise you're definitely right, using
C code makes more sense.

> I see two implementations of memcpy() under arch/x86/boot.
> 
> One is in copy.S. This is assembly code and looks like is supposed to
> run in 16bit mode. (code16).
> 
> Other one is in compressed/misc.c and there are two definitions, one
> for 32bit and one fore 64bit.

They are basically the 16-, 32-, and 64-bit variants of the same code.

> I am not sure why there is a need to write memcpy() in assembly when
> C will do just fine for my case. I don't have to write two versions of
> memcpy() and use it both for 32bit and 64bit.

The point would be to use the ones we already have.

> So I can just make all the purgatory code share same version of memcpy(),
> memcmp() and memset(), is that fine. I have taken implementations of
> these functions from lib/string.c

It depends on if you care about performance.  For memcpy() and memset()
in particular, the CPU has internally optimized versions of these that
beats C at least on any newer silicon.

	-hpa


  reply	other threads:[~2014-02-25 16:56 UTC|newest]

Thread overview: 106+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-01-27 18:57 [RFC PATCH 00/11][V2] kexec: A new system call to allow in kernel loading Vivek Goyal
2014-01-27 18:57 ` Vivek Goyal
2014-01-27 18:57 ` [PATCH 01/11] kexec: Move segment verification code in a separate function Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-01-27 18:57 ` [PATCH 02/11] resource: Provide new functions to walk through resources Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-01-27 18:57 ` [PATCH 03/11] bin2c: Move bin2c in scripts/basic Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-01-27 21:12   ` Michal Marek
2014-01-27 21:12     ` Michal Marek
2014-01-27 21:18     ` Vivek Goyal
2014-01-27 21:18       ` Vivek Goyal
2014-01-27 21:54       ` Michal Marek
2014-01-27 21:54         ` Michal Marek
2014-01-27 18:57 ` [PATCH 04/11] kernel: Build bin2c based on config option CONFIG_BUILD_BIN2C Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-01-27 18:57 ` [PATCH 05/11] kexec: Make kexec_segment user buffer pointer a union Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-01-27 18:57 ` [PATCH 06/11] kexec: A new system call, kexec_file_load, for in kernel kexec Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-02-21 14:59   ` Borislav Petkov
2014-02-21 14:59     ` Borislav Petkov
2014-02-24 16:41     ` Vivek Goyal
2014-02-24 16:41       ` Vivek Goyal
2014-02-25 19:35       ` Petr Tesarik
2014-02-25 19:35         ` Petr Tesarik
2014-02-25 21:47         ` Borislav Petkov
2014-02-25 21:47           ` Borislav Petkov
2014-02-26 15:37       ` Borislav Petkov
2014-02-26 15:37         ` Borislav Petkov
2014-02-26 15:46         ` Vivek Goyal
2014-02-26 15:46           ` Vivek Goyal
2014-01-27 18:57 ` [PATCH 07/11] kexec: Create a relocatable object called purgatory Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-02-24 19:08   ` H. Peter Anvin
2014-02-24 19:08     ` H. Peter Anvin
2014-02-25 16:43     ` Vivek Goyal
2014-02-25 16:43       ` Vivek Goyal
2014-02-25 16:55       ` H. Peter Anvin [this message]
2014-02-25 16:55         ` H. Peter Anvin
2014-02-25 18:20         ` Vivek Goyal
2014-02-25 18:20           ` Vivek Goyal
2014-02-25 21:09           ` H. Peter Anvin
2014-02-25 21:09             ` H. Peter Anvin
2014-02-26 14:52             ` Vivek Goyal
2014-02-26 14:52               ` Vivek Goyal
2014-02-26 16:00   ` Borislav Petkov
2014-02-26 16:00     ` Borislav Petkov
2014-02-26 16:32     ` Vivek Goyal
2014-02-26 16:32       ` Vivek Goyal
2014-02-27 15:44       ` Borislav Petkov
2014-02-27 15:44         ` Borislav Petkov
2014-01-27 18:57 ` [PATCH 08/11] kexec-bzImage: Support for loading bzImage using 64bit entry Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-02-25 18:38   ` H. Peter Anvin
2014-02-25 18:38     ` H. Peter Anvin
2014-02-25 18:43     ` Vivek Goyal
2014-02-25 18:43       ` Vivek Goyal
2014-02-27 21:36   ` Borislav Petkov
2014-02-27 21:36     ` Borislav Petkov
2014-02-28 16:31     ` Vivek Goyal
2014-02-28 16:31       ` Vivek Goyal
2014-03-05 16:37       ` Borislav Petkov
2014-03-05 16:37         ` Borislav Petkov
2014-03-05 16:40         ` H. Peter Anvin
2014-03-05 16:40           ` H. Peter Anvin
2014-03-05 18:40         ` Vivek Goyal
2014-03-05 18:40           ` Vivek Goyal
2014-03-05 19:47           ` Borislav Petkov
2014-03-05 19:47             ` Borislav Petkov
2014-01-27 18:57 ` [PATCH 09/11] kexec: Provide a function to add a segment at fixed address Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-02-27 21:52   ` Borislav Petkov
2014-02-27 21:52     ` Borislav Petkov
2014-02-28 16:56     ` Vivek Goyal
2014-02-28 16:56       ` Vivek Goyal
2014-03-10 10:01       ` Borislav Petkov
2014-03-10 10:01         ` Borislav Petkov
2014-03-10 15:35         ` Vivek Goyal
2014-03-10 15:35           ` Vivek Goyal
2014-01-27 18:57 ` [PATCH 10/11] kexec: Support for loading ELF x86_64 images Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-02-28 14:58   ` Borislav Petkov
2014-02-28 14:58     ` Borislav Petkov
2014-02-28 17:11     ` Vivek Goyal
2014-02-28 17:11       ` Vivek Goyal
2014-03-07 17:12       ` Borislav Petkov
2014-03-07 17:12         ` Borislav Petkov
2014-03-07 18:39         ` Borislav Petkov
2014-03-07 18:39           ` Borislav Petkov
2014-03-10 14:42           ` Vivek Goyal
2014-03-10 14:42             ` Vivek Goyal
2014-03-12 16:19             ` Borislav Petkov
2014-03-12 16:19               ` Borislav Petkov
2014-03-12 17:24               ` Vivek Goyal
2014-03-12 17:24                 ` Vivek Goyal
2014-01-27 18:57 ` [PATCH 11/11] kexec: Support for Kexec on panic using new system call Vivek Goyal
2014-01-27 18:57   ` Vivek Goyal
2014-02-28 17:28   ` Borislav Petkov
2014-02-28 17:28     ` Borislav Petkov
2014-02-28 21:06     ` Vivek Goyal
2014-02-28 21:06       ` Vivek Goyal
2014-05-26  8:25 ` [RFC PATCH 00/11][V2] kexec: A new system call to allow in kernel loading Borislav Petkov
2014-05-26  8:25   ` Borislav Petkov
2014-05-27 12:34   ` Vivek Goyal
2014-05-27 12:34     ` Vivek Goyal

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