[Question about KVM on arm64] Consider putting VINVALL to deactivation

Marc Zyngier maz at kernel.org
Wed Jan 15 05:50:58 PST 2020


Hi Shaokun,

On 2020-01-14 14:20, Shaokun Zhang wrote:
> Hi Marc,
> 
> On activation, VMAPP command is followed by a VINVALL, which could be
> quite expensive for the start-up of virtual machine. If a vpeid is 
> allowed
> successfully, it is not used in system.

How expensive? This is exactly similar to what happens on a physical 
machine
where we perform an INVALL on MAPC. And yet you don't complain about 
that.

Please provide numbers.

> We may consider put VINVALL to deactivation to ensure all cache of 
> certain
> vpeid is invalid, to simplify activation. We consider start-up may be 
> more
> common and more time-consuming-sensitive than shutdown process.

In my world, they cost the same thing, and happen just as often. Also, I 
want
guarantees that on VMAPP, there is no stale information even if this is 
the
first time we're using this VPEid (who knows what happens over kexec, 
for
example).

> Do you think it's all right?

I don't, for the reasons stated above. You also provide no numbers 
showing
how bad the overhead is, so I'm left guessing.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...



More information about the linux-arm-kernel mailing list