On 11/27/19 4:34 AM, Jürgen Groß wrote:
> On 26.11.19 18:30, George Dunlap wrote:
>> On 11/26/19 5:17 PM, George Dunlap wrote:
>>> - xl will use the libxl default for maptrack, but does its own default
>>> calculation for grant frames: either 32 or 64, based on the max
>>> possible mfn.
>>
>> [snip]
>>
>>> @@ -199,13 +198,6 @@ static void parse_global_config(const char
>>> *configfile,
>>> if (!xlu_cfg_get_long (config, "max_grant_frames", &l, 0))
>>> max_grant_frames = l;
>>> - else {
>>> - libxl_physinfo_init(&physinfo);
>>> - max_grant_frames = (libxl_get_physinfo(ctx, &physinfo) != 0 ||
>>> - !(physinfo.max_possible_mfn >> 32))
>>> - ? 32 : 64;
>>> - libxl_physinfo_dispose(&physinfo);
>>> - }
>>
>> Sorry, meant to add a patch to add this functionality back into the
>> hypervisor -- i.e., so that opt_max_grant_frames would be 32 on systems
>> with 32-bit mfns.
>>
>> But this seems like a fairly strange calculation anyway; it's not clear
>> to me where it would have come from.
> mfns above the 32-bit limit require to use grant v2. This in turn
> doubles the grant frames needed for the same number of grants.
But is large mfns the *only* reason to use grant v2? Aren't modern
guests going to use grant v2 regardless of the max mfn size?
-George
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