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Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs u

from [Jan Beulich]

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To:	"Keir Fraser" <keir.xen@xxxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits
From:	"Jan Beulich" <JBeulich@xxxxxxxxxx>
Date:	Fri, 15 Apr 2011 08:08:42 +0100
Cc:	"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "winston.l.wang" <winston.l.wang@xxxxxxxxx>
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>>> On 14.04.11 at 18:48, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
> On 14/04/2011 17:28, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>> The only case not handled was if the TSC
>> overflowed 64 bits during the process - I considered this case
>> hypothetical only.
>> 
>> The final write of tsc+4*delta was basically an attempt to restore
>> the value that would have been there if we didn't fiddle with it.
> 
> But the write is actually tsc + 4*(s32)(tmp-tsc), and tmp has 1U<<32 ORed
> into it (because it was read after your second write to the TSC. Perhaps we
> should just write back the full original tsc and call that good enough?

Again, note the (s32) cast.

Jan


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RE: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, (continued) RE: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Dan Magenheimer Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Keir Fraser Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Jan Beulich Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Keir Fraser Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Jan Beulich Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Keir Fraser RE: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Wang, Winston L Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Keir Fraser RE: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Wang, Winston L Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Jan Beulich Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Jan Beulich <= Re: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Keir Fraser RE: [Xen-devel] [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits, Wang, Winston L

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