Re: [Xen-devel] [PATCH v10 09/25] x86: refactor psr: L3 CAT: set value: implement framework.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.04.17 at 13:44, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> On 17-04-13 05:31:41, Jan Beulich wrote:
>> >>> On 13.04.17 at 13:11, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
>> > On 17-04-13 04:58:06, Jan Beulich wrote:
>> >> >>> On 13.04.17 at 12:49, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
>> >> > How about a per socket array like this:
>> >> > uint32_t domain_switch[1024];
>> >> > 
>> >> > Every bit represents a domain id. Then, we can handle this case as 
>> >> > below:
>> >> > 1. In 'psr_cpu_init()', clear the array to be 0. I think this place is 
>> >> > enough to
>> >> >    cover socket offline case. We do not need to clear it in 
>> >> > 'free_socket_resources'.
>> >> > 
>> >> > 2. In 'psr_ctxt_switch_to()', test_and_set_bit(domain_id, 
>> >> > domain_switch) to set
>> >> >    the bit to 1 according to domain_id. If the old value is 0 and the 
>> >> >    'psr_cos_ids[socket]' is not 0, restore 'psr_cos_ids[socket]' to be 
>> >> > 0.
>> >> > 
>> >> > 3. In 'psr_set_val()', test_and_set_bit(domain_id, domain_switch) to 
>> >> > set the bit
>> >> >    to 1 too. Then, update 'psr_cos_ids[socket]' according to find/pick 
>> >> > flow.
>> >> > 
>> >> > Then, we only use 4KB for one socket.
>> >> 
>> >> This looks to come closer to something I'd consider acceptable, but
>> >> I may not understand your intentions in full yet: For one, there's
>> >> nowhere you clear the bit (other than presumably during socket
>> >> cleanup). 
>> > 
>> > Actually, clear the array in 'free_socket_resources' has same effect. I can
>> > move clear action into it.
>> 
>> That wasn't my point - I was asking about clearing individual bits.
>> Point being that if you only ever set bits in the map, you'll likely
>> end up iterating through all active domains anyway.
>> 
> If entering 'free_socket_resources', that means no more actions to
> the array on this socket except clearing it. Can I just memset this array
> of the socekt to 0?

You can, afaict, but unless first you act on the set bits I can't see why
you would want to track the bits in the first place. Or maybe I'm still
not understanding your intention, in which case I guess the best you
can do is simply implement your plan, and we'll discuss it in v11 review.

Jan


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