Re: Slow Kernel Boot

[Izik Eidus <izike-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

On Tue, 2008-01-08 at 18:31 +0530, Amit Shah wrote:
> On Tuesday 08 January 2008 12:12:53 Amit Shah wrote:
> > On Tuesday 08 January 2008 03:35:48 Dave Hansen wrote:
> > > With kvm-44, I thought my kernel was freezing during boot if I gave it
> > > 1G of RAM.  But, it boots fine with 512M.
> > >
> > > So, I instrumented the kernel, and found out that it is just taking a
> > > long time to memset a 58MB area of memory for mem_map[].  It appears to
> > > be taking a mmio_exit for every access of every byte of memory.  The end
> > > result is a ~100kbps memset() speed.  Yes, 100 kilobytes/sec.
> > >
> > > I just tried kvm from git, and the kernel doesn't even get that far.  I
> > > see this in debugfs
> > >
> > > 	insn_emulation:1393985
> > >
> > > even before I get a single kernel message.  And it keeps going up, fast.
> > > I can get the kernel to boot just fine if I give it less than 896MB of
> > > RAM.
> > >
> > > kvm-44 boots long enough for me to see a really funky e820 table:
> > >
> > > BIOS-provided physical RAM map:
> > >  BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
> > >  BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
> > >  BIOS-e820: 00000000000e8000 - 0000000000100000 (reserved)
> > >  BIOS-e820: 0000000000100000 - 00000000fffbd000 (usable)
> > >  BIOS-e820: 00000000fffbd000 - 00000000ffff0000 (reserved)
> > >
> > > Note that this is with '-m 1G'!!  It looks to me like one of those
> >
> > And there lies the problem. qemu doesn't understand suffixes like 'G'. If
> > you pass -m 1024, you'll boot just fine.
> >
> > This is really annoying of qemu (it should either accept that input
> > properly or bail out); a patch is welcome!
> 
> Just wrote this.
> 
> From 575b4414314cdc5c8280cfbf1761a6d419dd7a40 Mon Sep 17 00:00:00 2001
> From: Amit Shah <amit.shah-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
> Date: Tue, 8 Jan 2008 18:24:34 +0530
> Subject: [PATCH] qemu: Add support for suffixes to the -m parameter
> 
> The -m parameter doesn't take suffixes like G or M currently
> and it doesn't complain if such a suffix is given.
> 
> Add support for the G and M suffixes and update the usage
> instructions appropriately.
> 
> Signed-off-by: Amit Shah <amit.shah-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
> ---
>  qemu/vl.c |   25 +++++++++++++++++++++++--
>  1 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/qemu/vl.c b/qemu/vl.c
> index 0f023ac..114a84e 100644
> --- a/qemu/vl.c
> +++ b/qemu/vl.c
> @@ -7927,7 +7927,9 @@ static void help(int exitcode)
>  #ifdef TARGET_I386
>             "-no-fd-bootchk  disable boot signature checking for floppy 
> disks\n"
>  #endif
> -           "-m megs         set virtual RAM size to megs MB [default=%d]\n"
> +           "-m size         set virtual RAM size to size megs [default=%d 
> MB].\n"
> +           "                Optional suffixes 'M' (megabyte) and 'G' 
> (gigabyte)"
> +                            " are supported\n"
>             "-smp n          set the number of CPUs to 'n' [default=1]\n"
>             "-nographic      disable graphical output and redirect serial I/Os 
> to console\n"
>             "-portrait       rotate graphical output 90 deg left (only PXA 
> LCD)\n"
> @@ -8858,7 +8860,26 @@ int main(int argc, char **argv)
>                  help(0);
>                  break;
>              case QEMU_OPTION_m:
> -                ram_size = (int64_t)atoi(optarg) * 1024 * 1024;
> +                errno = 0;
> +                ram_size = strtoul(optarg, &optarg, 0);
> +                if (errno)
> +                    help(1);
> +                switch (*optarg) {
> +                case 'G':
> +                case 'g':
> +                    ram_size *= 1024;
> +                    /* fall through */
> +                case 'M':
> +                case 'm':
> +                case '\0':
> +                    ram_size *= 1024 * 1024;
> +                    optarg++;
> +                    break;
> +                default:
> +                    help(1);
> +                    break;
> +                }
> +
>                  if (ram_size <= 0)
>                      help(1);
>                  if (ram_size > PHYS_RAM_MAX_SIZE) {
i guess you should send it to qemu-devel, and then it will be merged to
kvm from there


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