Message-ID: <4731BAB2.9040004@redhat.com>
Date: Wed, 07 Nov 2007 11:16:34 -0200
From: Glauber de Oliveira Costa <gcosta@redhat.com>
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To: Akio Takebe <takebe_akio@jp.fujitsu.com>
CC: linux-kernel@vger.kernel.org, jeremy@goop.org, hollisb@us.ibm.com,
       kvm-devel@lists.sourceforge.net, avi@qumranet.com
Subject: Re: [kvm-devel] include files for kvmclock
References: <11943875362987-git-send-email-gcosta@redhat.com> <11943875433821-git-send-email-gcosta@redhat.com> <1DC8211684B62Btakebe_akio@jp.fujitsu.com>
In-Reply-To: <1DC8211684B62Btakebe_akio@jp.fujitsu.com>
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Akio Takebe escreveu:
> Hi, Glauber
> 
> This is interesting facility. :-)
> 
>> +#define KVM_HCALL_REGISTER_CLOCK	1
>> +
>> +union kvm_hv_clock {
>> +	struct {
>> +		u64 tsc_mult;
>> +		u64 now_ns;
>> +		/* That's the wall clock, not the water closet */
>> +		u64 wc_sec;
>> +		u64 wc_nsec;
>> +		u64 last_tsc;
>> +		/* At first, we could use the tsc value as a marker, but Jeremy
>> +		 * well noted that it will cause us locking problems in 32-bit
>> +		 * sys, so we have a special version field */
>> +		u32 version;
>> +	};
>> +	char page_align[PAGE_SIZE];
>> +};
>> +
> Why does kvm_hv_clock need page_align?
Each vcpu will register a page on its own. In the guest side, it will be
an array of pages. So, we make it page sized.

> And also the kvm_hv_clock is alloced with kvm_vcpu,
There's no requirements on the host part at all. So it doesn't really
matter. In the next version, I may make it even a simple pointer.

> so the align is not enough, isn't it?
> I thik __atribute__((__aligne__(PAGE_SIZE)))) is better than it.
It deals with the start of the structure, but not with its size. See the
guest part: Where it matters, I do use it.


Thanks

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