15 messages in com.xensource.lists.xen-ia64-develRE: [Xen-ia64-devel] [PATCH] NEW_TLBF...
FromSent OnAttachments
Kouya SHIMURA26 Jan 2007 03:05.patch
Alex Williamson26 Jan 2007 15:06 
Xu, Anthony28 Jan 2007 22:30 
Isaku Yamahata28 Jan 2007 23:35 
Kouya SHIMURA29 Jan 2007 00:09 
Xu, Anthony29 Jan 2007 00:59 
Isaku Yamahata29 Jan 2007 01:03 
Isaku Yamahata29 Jan 2007 01:20 
Xu, Anthony29 Jan 2007 01:58 
Isaku Yamahata29 Jan 2007 02:28 
Kouya SHIMURA29 Jan 2007 02:30 
Xu, Anthony29 Jan 2007 17:45 
Isaku Yamahata29 Jan 2007 19:35 
Xu, Anthony29 Jan 2007 20:16 
Isaku Yamahata29 Jan 2007 21:16 
Subject:RE: [Xen-ia64-devel] [PATCH] NEW_TLBFLUSH_CLOCK_PERIOD_SOFTIRQ is notregistered.
From:Xu, Anthony (anth@intel.com)
Date:01/29/2007 08:16:30 PM
List:com.xensource.lists.xen-ia64-devel

Isaku Yamahata write on 2007年1月30日 11:36:

On Tue, Jan 30, 2007 at 09:46:04AM +0800, Xu, Anthony wrote:

Isaku Yamahata write on 2007年1月29日 18:29:

How about the following example? For simplicity, we consider only local_flush_tlb_all(). (The similar argument can be applied to vcpu_vhpt_flush())

suppose domM has two vcpus, vcpu0, vcpu1. domN has one vcpu, vcpu2.

- case 1 vcpu0 and vcpu1 are running on same pcpu. vcpu0 runs. context switch <<<< local_flush_tlb_all() is necessry here vcpu1 runs.

- case 2 vcpu0, vcpu1 and vcpu2 are running on the same pcpu vcpu0 runs context switch vcpu2 runs vcpu2 issues local_tlb_flush(). context switch <<< local_flush_tlb_all() can be skipped.

I can understand this. Yes, this local_flush_tlb_all can be skipped, But it is because vcpu2 issues local_tlb_flush. My question is why we need new_tlbflush_clock_period?

Because the counter is finite. If we can ignore conter overflow, we can check only which counter is bigger. But when overflow comes in (i.e. counter == 0 after increment), things become complicated. It's the reason of new_tlbflush_clock_period.

Probably another approach to address overflow is to use signed comparison like Linux jiffies time_after(). But we can't assume the distance between two conters is near enough.

Understand now. One more question

Why need local_vhpt_flush and vcpu_vhpt_flush call
tlbflush_clock_inc_and_return?

In per-CPU VHPT mode, tlbflush_clock_inc_and_return only needs to be called in local_flush_tlb_all.

Am I right?

Thanks, Anthony

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