On 27.02.20 14:24, Christian Borntraeger wrote:
On 27.02.20 13:43, Michael Mueller wrote:
On 27.02.20 13:27, Christian Borntraeger wrote:
On 27.02.20 10:10, Michael Mueller wrote:
The boolean module parameter "kvm.use_gisa" controls if newly
created guests will use the GISA facility if provided by the
host system. The default is yes.
# cat /sys/module/kvm/parameters/use_gisa
Y
The parameter can be changed on the fly.
# echo N > /sys/module/kvm/parameters/use_gisa
Already running guests are not affected by this change.
The kvm s390 debug feature shows if a guest is running with GISA.
# grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
...
00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
In general, that value should not be changed as the GISA facility
enhances interruption delivery performance.
A reason to switch the GISA facility off might be a performance
comparison run or debugging.
Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
Looks good to me. Regarding the other comments, I think allowing for dynamic changes
and keeping use_gisa vs disable_gisa makes sense. So I would think that the patch
as is makes sense.
The only question is: shall we set use_gisa to 0 when the machine does not support
it (e.g. VSIE?) and then also forbid setting it to 1? Could be overkill.
Then I would rename the parameter to "try_to_use_gisa" instead. (a joke ;) )
In that case we exit gisa_init() because of the missing AIV facility.
void kvm_s390_gisa_init(struct kvm *kvm)
{
struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
--> if (!css_general_characteristics.aiv)
return;
gi->origin = &kvm->arch.sie_page2->gisa;
gi->alert.mask = 0;
...
}
I know. My point was more: "can we expose this". But this is probably overkill.
I agree with Connie here, that would make the whole thing
just more error-prone. That way the messages are at least
consistent.
