[Xen-devel] RE: [Xen-ia64-devel] flush_tlb_mask and grant_table on ia64

["Xu, Anthony" <anthony.xu@xxxxxxxxx>]

>From: xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx
>[mailto:xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Tristan
>Gingold
>Sent: 2006?4?21? 15:24
>To: xen-devel@xxxxxxxxxxxxxxxxxxx; xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
>Subject: [Xen-ia64-devel] flush_tlb_mask and grant_table on ia64
>
>Hi,
>
>on IA64 flushing the whole TLB is very expensive: this is a cpu tlb flush and
>clearing 16MB of memory (virtual tlb).
>However, flushing an address range is rather cheap.  Flushing an address range
>on every processors is also cheap (no IPI).
>
>Unfortunatly Xen common code flushes the whole TLB after unmapping grant
>reference.
>
Agreed

>Currently, this is not done on IA64 because domain_dirty_cpumask is never set
>(bug!).
>
>We can flush TLB by range within destroy_grant_host_mapping.  But then we need
>to disable the flush_tlb_mask call.
>
>What is the best solution?
>
It depends on the coverage of VHPT and coverage of purged page.
Linux kernel also use this,
If coverage of purged page is less than a fixed value, 
flush TLB by range.
If coverage of purged page is larger than a fixed value,
Flush the whole TLB.

>Thank you for comments,
>Tristan.
>
>
>
>
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