On 15/05/18 09:25, Jan Beulich wrote: >>>> On 26.04.18 at 12:52, <[email protected]> wrote: >>>>> On 26.04.18 at 11:51, <[email protected]> wrote: >>> On 26/04/18 10:41, Jan Beulich wrote: >>>> --- a/xen/arch/x86/mm.c >>>> +++ b/xen/arch/x86/mm.c >>>> @@ -1202,11 +1202,23 @@ void put_page_from_l1e(l1_pgentry_t l1e, >>>> unlikely(((page->u.inuse.type_info & PGT_count_mask) != 0)) >>>> && >>>> (l1e_owner == pg_owner) ) >>>> { >>>> + cpumask_t *mask = this_cpu(scratch_cpumask); >>>> + >>>> + cpumask_clear(mask); >>>> + >>>> for_each_vcpu ( pg_owner, v ) >>>> { >>>> - if ( pv_destroy_ldt(v) ) >>>> - flush_tlb_mask(cpumask_of(v->dirty_cpu)); >>>> + unsigned int cpu; >>>> + >>>> + if ( !pv_destroy_ldt(v) ) >>>> + continue; >>>> + cpu = read_atomic(&v->dirty_cpu); >>>> + if ( is_vcpu_dirty_cpu(cpu) ) >>>> + __cpumask_set_cpu(cpu, mask); >>>> } >>>> + >>>> + if ( !cpumask_empty(mask) ) >>>> + flush_tlb_mask(mask); >>> Thinking about this, what is wrong with: >>> >>> bool flush; >>> >>> for_each_vcpu ( pg_owner, v ) >>> if ( pv_destroy_ldt(v) ) >>> flush = true; >>> >>> if ( flush ) >>> flush_tlb_mask(pg_owner->dirty_cpumask); >>> >>> This is far less complicated cpumask handling. As the loop may be long, >>> it avoids flushing pcpus which have subsequently switched away from >>> pg_owner context. It also avoids all playing with v->dirty_cpu. >> That would look to be correct, but I'm not sure it would be an improvement: >> While it may avoid flushing some CPUs, it may then do extra flushes on >> others (which another vCPU of the domain has been switched to). Plus it >> would flush even those CPUs where pv_destroy_ldt() has returned false, >> as long as the function returned true at least once. > Ping?
I'm not sure it is worth trying to optimise this code. I've got a patch for 4.12 to leave it compiled out by default. Therefore, Acked-by: Andrew Cooper <[email protected]> on the original patch. _______________________________________________ Xen-devel mailing list [email protected] https://lists.xenproject.org/mailman/listinfo/xen-devel
