Re: [PATCH v16 08/14] numa: Extend CLI to provide memory latency and bandwidth information

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 20 Nov 2019 15:55:04 +0800
Tao Xu <tao3.xu@intel.com> wrote:

> On 11/19/2019 7:03 PM, Igor Mammedov wrote:
> > On Fri, 15 Nov 2019 15:53:46 +0800
> > Tao Xu <tao3.xu@intel.com> wrote:
> >   
> >> From: Liu Jingqi <jingqi.liu@intel.com>
> >>
> >> Add -numa hmat-lb option to provide System Locality Latency and
> >> Bandwidth Information. These memory attributes help to build
> >> System Locality Latency and Bandwidth Information Structure(s)
> >> in ACPI Heterogeneous Memory Attribute Table (HMAT).
> >>
> >> Signed-off-by: Liu Jingqi <jingqi.liu@intel.com>
> >> Signed-off-by: Tao Xu <tao3.xu@intel.com>  
> > 
> > looks good to me, so
> > 
> > Reviewed-by: Igor Mammedov <imammedo@redhat.com>
> > 
> > 
> > PS:
> > also see question below
> >   
> [...]
> >> +
> >> +        hmat_lb->range_bitmap |= node->bandwidth;
> >> +        first_bit = ctz64(hmat_lb->range_bitmap);
> >> +        hmat_lb->base = UINT64_C(1) << first_bit;
> >> +        max_entry = node->bandwidth / hmat_lb->base;
> >> +        last_bit = 64 - clz64(hmat_lb->range_bitmap);
> >> +
> >> +        /*
> >> +         * For bandwidth, first_bit record the base unit of bandwidth bits,
> >> +         * last_bit record the last bit of the max bandwidth. The max compressed
> >> +         * bandwidth should be less than 0xFFFF (UINT16_MAX)
> >> +         */
> >> +        if ((last_bit - first_bit) > UINT16_BITS || max_entry >= UINT16_MAX) {  
> >                                                         ^^^^^^^^^^^^^^^^^^^
> > what bandwidth combination is going to trigger above condition?
> >   
> Only use (last_bit - first_bit) > UINT16_BITS, we can't trigger error if 
> the max compressed bandwidth is 0xFFFF. Because in that condition, 
> "last_bit - first_bit == UINT16_BITS". So I add "max_entry >= 
> UINT16_MAX" to catch 0xFFFF. For example:
> 
> Combination 1 (Error):
> bandwidth1   = ...0000 1111 1111 1111 1110 0000... (max_entry 32767)
> range_bitmap = ...0000 1111 1111 1111 1110 0000... (range is 15 bits)
> bandwidth2   = ...0000 1111 1111 1111 1111 0000... (max_entry 65535)
> range_bitmap = ...0000 1111 1111 1111 1111 0000... (range is 16 bits)
> 
> Combination 2 (Error):
> bandwidth1   = ...0000 1111 1111 1111 1110 0000... (max_entry 32767)
> range_bitmap = ...0000 1111 1111 1111 1110 0000... (range is 15 bits)
> bandwidth2   = ...0001 1111 1111 1111 1110 0000... (max_entry 65535)
> range_bitmap = ...0001 1111 1111 1111 1110 0000... (range is 16 bits)
> 
> Combination 3 (OK, because bandwidth1 will be compressed to 65534):
> bandwidth1   = ...0000 1111 1111 1111 1110 0000... (max_entry 32767)
> range_bitmap = ...0000 1111 1111 1111 1110 0000... (range is 15 bits)
> bandwidth2   = ...0000 0111 1111 1111 1111 0000... (max_entry 32767)
> range_bitmap = ...0000 1111 1111 1111 1111 0000... (range is 16 bits)
> 
> Combination 4 (Error):
> bandwidth1   = ...0000 1111 1111 1111 1111 0000... (max_entry 65535)
> range_bitmap = ...0000 1111 1111 1111 1111 0000... (range is 16 bits)

ok, I'd use in max/min possible values in bios-tables-test,
to make sure that we are testing whole range and would be able
to detect a error in case the valid ranges regressed (shrink)
and x-fail tests I've asked for in QMP test should detect
error other way around.