Re: [Xen-devel] [PATCH v3 ]libxl: allow to set more than 31 vcpus

[Dario Faggioli <raistlin@xxxxxxxx>]

On Fri, 2012-06-01 at 02:48 +0000, Zhang, Yang Z wrote: 
> Change from v2:
> Add function libxl_cpumap_to_hex_string to covert cpumap to hex string.
> According to Ian's comments, modified some codes to make the logic more 
> reasonable.
> 
> In current implementation, it uses integer to record current avail cpus and 
> this only allows user to specify 31 vcpus. 
> In following patch, it uses cpumap instead integer which make more sense than 
> before. Also there is no limit to the max vcpus.
> 
This part I understand, and looks reasonable.

I also see this is the whole point of your other patch, however ...

> diff -r 3b0eed731020 tools/libxl/xl_cmdimpl.c
> --- a/tools/libxl/xl_cmdimpl.c  Fri Jun 01 09:27:17 2012 +0800
> +++ b/tools/libxl/xl_cmdimpl.c  Fri Jun 01 10:34:13 2012 +0800
> @@ -650,7 +650,14 @@ static void parse_config_data(const char
> 
>      if (!xlu_cfg_get_long (config, "vcpus", &l, 0)) {
>          b_info->max_vcpus = l;
> -        b_info->cur_vcpus = (1 << l) - 1;
> +
> +        if (libxl_cpumap_alloc(ctx, &b_info->avail_vcpus, l)) {
> +            fprintf(stderr, "Unable to allocate cpumap\n");
> +            exit(1);
> +        }
>
... Do you mind explaining me what would have happened here without your
previous patch, i.e., by just using the existing libxl_cpumap_alloc ?

I might be wrong, but I was wondering whether it is worth changing the
interface like that for just this single case which saves, what, 1 to 3
bytes per domain?

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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