linux-kernel - Re: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation

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Date:	Thu, 12 Jul 2007 16:28:54 +0000
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Pavel Machek <pavel@....cz>
Cc:	nigel@...el.suspend2.net, "Rafael J. Wysocki" <rjw@...k.pl>,
	Jeremy Maitin-Shepard <jbms@....edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH 0/2] Kexec jump: The first step to kexec base
	hibernation

On Wed, 2007-07-11 at 13:13 +0200, Pavel Machek wrote:
> Hi!
> 
> Looks interesting... but I was feeling strange dejavu reading
> this... and that's because you pasted the changelog twice :-).
> 

Sorry, I should have re-checked the mail before sending out.

> How fast can kexec boot secondary kernel?

I measure it on my IBM T42 with CONFIG_PRINTK_TIME=y. The boot-up time
is about 4.35s from kexec is issued to root mounted in kexec kernel.

I think it is possible to optimize. Maybe the kexec kernel can
be hibernate/resume by the normal kernel too. This way, a real
kexec/boot-up is only needed for the first time.

> > 2. Compile the kexec-tools with kdump and kjump patches added, the
> >    kdump patch can be found at:
> > 
> > http://lse.sourceforge.net/kdump/patches/kexec-tools-1.101-dkump10.patch
> 
> I got 404 error :-(.

Sorry, typo problem. The URL should be:
http://lse.sourceforge.net/kdump/patches/kexec-tools-1.101-kdump10.patch

> > 3. Boot compiled kernel, the reserved crash kernel memory region must
> >    be added to kernel command line as following:
> > 
> >    crashkernel=<XX>M@<XX>M
> > 
> >    Where, <XX> should be replaced by the real memory size and position.
> 
> How much memory do you suggest to reserve? 64M? 

I reserved 16M RAM. I think this is sufficient for a simple disk based
hibernation.

> > 7. In the kexec booted kernel, trigger the jumping back with following
> >    shell command.
> > 
> >    echo <a>:<b> > /sys/power/resume
> > 
> >    Where <a> and <b> is non-negative integer, at least one of them must
> >    be non-zero.
> 
> What does a and b mean?
> 

a and b has no meaning. They are only used to trigger the resume
process. This will be fixed in the future version.

> > +/* Adds the kexec_backup= command line parameter to command line. */
> > +static int cmdline_add_backup(char *cmdline, unsigned long addr)
> > +{
> > +	int cmdlen, len, align = 1024;
> > +	char str[30], *ptr;
> > +
> > +	/* Passing in kexec_backup=xxxK format. Saves space required in cmdline.
> > +	 * Ensure 1K alignment*/
> > +	if (addr%align)
> > +		return -1;
> > +	addr = addr/align;
> > +	ptr = str;
> > +	strcpy(str, " kexec_backup=");
> > +	ptr += strlen(str);
> > +	ultoa(addr, ptr);
> > +	strcat(str, "K");
> > +	len = strlen(str);
> > +	cmdlen = strlen(cmdline) + len;
> > +	if (cmdlen > (COMMAND_LINE_SIZE - 1))
> > +		die("Command line overflow\n");
> > +	strcat(cmdline, str);
> > +#if 0
> > +		printf("Command line after adding backup\n");
> > +		printf("%s\n", cmdline);
> > +#endif
> > +	return 0;
> > +}
> 
> printf()? ...and please remove out commented code.

This is patch against kexec-tools, which is a userspace tool. So printf
is used. The commented code is just as other cmdline_add_xxx functions
of kexec-tools. But it is useless, and should be removed.

Best Regards,
Huang Ying
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