RE: [Xen-devel] [PATCH] When flush tlb , we need consider the cpu_online_map

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

>-----Original Message-----
>From: Jan Beulich [mailto:JBeulich@xxxxxxxxxx]
>Sent: Monday, March 29, 2010 8:55 PM
>To: Jiang, Yunhong
>Cc: Keir Fraser; xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [Xen-devel] [PATCH] When flush tlb , we need consider the
>cpu_online_map
>
>>>> "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> 29.03.10 14:00 >>>
>>When flush tlb mask, we need consider the cpu_online_map. The same happens to
>ept flush also.
>
>While the idea is certainly correct, doing this more efficiently seems
>quite desirable to me, especially when NR_CPUS is large:
>
>>--- a/xen/arch/x86/hvm/vmx/vmx.c      Sat Mar 27 16:01:35 2010 +0000
>>+++ b/xen/arch/x86/hvm/vmx/vmx.c      Mon Mar 29 17:49:51 2010 +0800
>>@@ -1235,6 +1235,9 @@ void ept_sync_domain(struct domain *d)
>>      * unnecessary extra flushes, to avoid allocating a cpumask_t on the 
>> stack.
>>      */
>>     d->arch.hvm_domain.vmx.ept_synced = d->domain_dirty_cpumask;
>>+    cpus_and(d->arch.hvm_domain.vmx.ept_synced,
>>+             d->arch.hvm_domain.vmx.ept_synced,
>>+             cpu_online_map);
>
>The added code can be combined with the pre-existing line:
>
>    cpus_and(d->arch.hvm_domain.vmx.ept_synced,
>             d->domain_dirty_cpumask, cpu_online_map);
>

Oops, really stupid and thanks for point out this.

>>     on_selected_cpus(&d->arch.hvm_domain.vmx.ept_synced,
>>                      __ept_sync_domain, d, 1);
>> }
>>--- a/xen/arch/x86/smp.c      Sat Mar 27 16:01:35 2010 +0000
>>+++ b/xen/arch/x86/smp.c      Mon Mar 29 17:47:25 2010 +0800
>>@@ -229,6 +229,7 @@ void flush_area_mask(const cpumask_t *ma
>>     {
>>         spin_lock(&flush_lock);
>>         cpus_andnot(flush_cpumask, *mask,
>*cpumask_of(smp_processor_id()));
>>+        cpus_and(flush_cpumask, cpu_online_map, flush_cpumask);
>
>Here, first doing the full-mask operation and then clearing the one
>extra bit is less overhead:
>
>        cpus_and(flush_cpumask, *mask, cpu_online_map);
>        cpu_clear(smp_processor_id(), flush_cpumask);

Good point.

--jyh

>
>>         flush_va      = va;
>>         flush_flags   = flags;
>>         send_IPI_mask(&flush_cpumask, INVALIDATE_TLB_VECTOR);
>
>Jan
>
>


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