RE: [Xen-devel] [PATCH] TSC scaling for live migration betweenplatforms with different TSC frequecies

["Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>]

Jan Beulich wrote:
>>>> "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx> 18.06.09 04:56 >>>
>> PATCH 0003-- Scaling host TSC freqeuncy patch.
> 
>> +int hvm_gtsc_need_scale(struct domain *d)
>> +{
>> +    uint32_t gtsc_khz;
>> +
>> +    gtsc_khz = d->arch.hvm_domain.gtsc_khz / 1000;
> 
> Can the variable please be renamed to what it contains (i.e.
> gtsc_mhz)? 
> 
>> u64 hvm_get_guest_tsc(struct vcpu *v)
>> {
>> -    u64 host_tsc;
>> -
>> -    if ( opt_softtsc )
>> -        host_tsc = hvm_get_guest_time(v);
>> -    else
>> -        rdtscll(host_tsc);
>> -
>> -    return host_tsc + v->arch.hvm_vcpu.cache_tsc_offset;
>> +    u64 host_tsc, scaled_htsc;
>> +
>> +    rdtscll(host_tsc);
>> +    scaled_htsc = hvm_h2g_scale_tsc(v, host_tsc);
>> +
>> +    return scaled_htsc + v->arch.hvm_vcpu.cache_tsc_offset; }
>> 
>> void hvm_migrate_timers(struct vcpu *v)
> 
> I'm getting the impression that the opt_softtsc functionality got
> lost here.

I am still confused by opt_softtsc check here. If want to use platform timer to 
emulate guest's tsc, hvm_set_guest_tsc should also need  perform this check to 
get correct cache_tsc_offset, but I didn't see it.   A bug ? 
If use host's tsc to emulate guest's tsc, the check is useless, so I removed it 
in my patch.  Maybe we need Dan's explanation about the check here to determin 
whether keep it or not.

> 
>> +        printk("Migrate to a platform with different freq:%ldMhz, "
>> +            "expected freq:%dMhz, enable rdtsc exiting!\n",
>> +                    cpu_khz / 1000, hdr->gtsc_khz / 1000);
> 
> gdprintk()? At least, I think, any guest related printk-s should
> identify which guest they're about. 

Added in the attached patch. Thanks!
Xiantao

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