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
next prev 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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