Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa

[Christian Borntraeger <borntraeger@de.ibm.com>]

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@linux.ibm.com>


Thanks applied.