Re: [Qemu-devel] [PATCH] vl: Adjust the place of calling mlockall to speedup VM's startup

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Sep 23, 2014 at 03:57:47PM +0800, zhanghailiang wrote:
> If we configure mlock=on and memory policy=bind at the same time,
> It will consume lots of time for system to treat with memory,
> especially when call mbind after mlockall.
> 
> Adjust the place of calling mlockall, calling mbind before mlockall
> can remarkably reduce the time of VM's startup.
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>

The idea makes absolute sense to me:
bind after lock will force data copy of
all pages. bind before lock gives us an
indication where to put data on fault in.

Acked-by: Michael S. Tsirkin <mst@redhat.com>


> ---
> Hi,
> 
> Actually, for mbind and mlockall, i have made a test about the time consuming 
> for the different call sequence. 
> 
> The results is shown below. It is obviously that mlockall called before mbind is 
> more time-consuming.
> 
> Besides, this patch is OK with memory hotplug.
> 
> TEST CODE:
>     if (mbind_first) {
>         printf("mbind --> mlockall\n");
>         mbind(ptr, ram_size/2, MPOL_BIND, &node0mask, 2,
>               MPOL_MF_STRICT | MPOL_MF_MOVE);
>         mbind(ptr + ram_size/2, ram_size/2, MPOL_BIND, &node1mask, 2,
>               MPOL_MF_STRICT | MPOL_MF_MOVE);
>         mlockall(MCL_CURRENT | MCL_FUTURE);
>     } else {
>         printf("mlockall --> mbind\n");
>         mlockall(MCL_CURRENT | MCL_FUTURE);
>         mbind(ptr, ram_size/2, MPOL_BIND, &node0mask, 2 ,
>               MPOL_MF_STRICT | MPOL_MF_MOVE);
>         mbind(ptr + ram_size/2, ram_size/2, MPOL_BIND, &node1mask, 2,
>               MPOL_MF_STRICT | MPOL_MF_MOVE);
>     }
> 
> RESULT 1:
> #time /home/test_mbind 10240 0
> memroy size 10737418240
> mlockall --> mbind
> 
> real    0m11.886s
> user    0m0.004s
> sys     0m11.865s
> #time /home/test_mbind 10240 1
> memroy size 10737418240
> mbind --> mlockall
> 
> real    0m5.334s
> user    0m0.000s
> sys     0m5.324s
> 
> RESULT 2:
> #time /home/test_mbind 4096 0
> memroy size 4294967296
> mlockall --> mbind
> 
> real    0m5.503s
> user    0m0.000s
> sys     0m5.492s
> #time /home/test_mbind 4096 1
> memroy size 4294967296
> mbind --> mlockall
> 
> real    0m2.139s
> user    0m0.000s
> sys     0m2.132s
> 
> Best Regards,
> zhanghailiang
> ---
>  vl.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/vl.c b/vl.c
> index dc792fe..adf4770 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -134,6 +134,7 @@ const char* keyboard_layout = NULL;
>  ram_addr_t ram_size;
>  const char *mem_path = NULL;
>  int mem_prealloc = 0; /* force preallocation of physical target memory */
> +int enable_mlock = false;
>  int nb_nics;
>  NICInfo nd_table[MAX_NICS];
>  int autostart;
> @@ -1421,12 +1422,8 @@ static void smp_parse(QemuOpts *opts)
>  
>  }
>  
> -static void configure_realtime(QemuOpts *opts)
> +static void realtime_init(void)
>  {
> -    bool enable_mlock;
> -
> -    enable_mlock = qemu_opt_get_bool(opts, "mlock", true);
> -
>      if (enable_mlock) {
>          if (os_mlock() < 0) {
>              fprintf(stderr, "qemu: locking memory failed\n");
> @@ -3973,7 +3970,7 @@ int main(int argc, char **argv, char **envp)
>                  if (!opts) {
>                      exit(1);
>                  }
> -                configure_realtime(opts);
> +                enable_mlock = qemu_opt_get_bool(opts, "mlock", true);
>                  break;
>              case QEMU_OPTION_msg:
>                  opts = qemu_opts_parse(qemu_find_opts("msg"), optarg, 0);
> @@ -4441,6 +4438,8 @@ int main(int argc, char **argv, char **envp)
>  
>      machine_class->init(current_machine);
>  
> +    realtime_init();
> +
>      audio_init();
>  
>      cpu_synchronize_all_post_init();
> -- 
> 1.7.12.4
>