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From: "Jan Beulich" <JBeulich@novell.com>
To: Keir Fraser <keir.xen@gmail.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
	"winston.l.wang" <winston.l.wang@intel.com>
Subject: Re: [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits
Date: Fri, 15 Apr 2011 08:08:42 +0100	[thread overview]
Message-ID: <4DA80B1A020000780003C875@vpn.id2.novell.com> (raw)
In-Reply-To: <C9CCE3EA.165CF%keir.xen@gmail.com>

>>> On 14.04.11 at 18:48, Keir Fraser <keir.xen@gmail.com> wrote:
> On 14/04/2011 17:28, "Jan Beulich" <JBeulich@novell.com> 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

  parent reply	other threads:[~2011-04-15  7:08 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-04-14  7:18 [PATCH] x86: don't write_tsc() non-zero values on CPUs updating only the lower 32 bits Jan Beulich
2011-04-14  7:25 ` Keir Fraser
2011-04-14  7:42   ` Jan Beulich
2011-04-14  7:50     ` Keir Fraser
2011-04-14  8:06       ` Jan Beulich
2011-04-14  9:18         ` Keir Fraser
2011-04-14 22:41           ` Dan Magenheimer
2011-04-15  6:40             ` Keir Fraser
2011-04-15 14:34               ` Dan Magenheimer
2011-04-15 17:28                 ` Keir Fraser
2011-04-14  7:28 ` Jan Beulich
2011-04-14 16:05 ` Keir Fraser
2011-04-14 16:28   ` Jan Beulich
2011-04-14 16:48     ` Keir Fraser
2011-04-14 18:33       ` Wang, Winston L
2011-04-14 21:06         ` Keir Fraser
2011-04-14 21:37           ` Wang, Winston L
2011-04-15  7:06           ` Jan Beulich
2011-04-15  7:08       ` Jan Beulich [this message]
2011-04-15  7:37         ` Keir Fraser
2011-04-15 14:49           ` Wang, Winston L

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