From: Keir Fraser <keir.fraser@eu.citrix.com>
To: "dan.magenheimer@oracle.com" <dan.magenheimer@oracle.com>,
"Xen-Devel (E-mail)" <xen-devel@lists.xensource.com>
Cc: Dave Winchell <dwinchell@virtualiron.com>
Subject: Re: [PATCH] strictly increasing hvm guest time
Date: Wed, 02 Jul 2008 17:07:34 +0100 [thread overview]
Message-ID: <C4916656.23741%keir.fraser@eu.citrix.com> (raw)
In-Reply-To: <20080702100358937.00000003744@djm-pc>
On 2/7/08 17:03, "Dan Magenheimer" <dan.magenheimer@oracle.com> wrote:
> This simple one-line patch changes hvm guest time from
> monotonically non-decreasing to monotonically strictly-
> increasing. As a result, two consecutive reads of the
> (virtual) hpet will never return the same value, thus
> avoiding the appearance that time has stopped (which may
> occur if there is skew between physical processor TSCs).
It does seem a little hack-ish, if we don't know of any issues arising from
the current code, and we expect cross-cpu deltas to be pretty small. Also
guests will often convert HPET reads to well-known units (e.g.,
microseconds, milliseconds) before using them, in which case even a delta of
one may not result in differing converted time values.
-- Keir
next prev parent reply other threads:[~2008-07-02 16:07 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-07-02 16:03 [PATCH] strictly increasing hvm guest time Dan Magenheimer
2008-07-02 16:07 ` Keir Fraser [this message]
2008-07-02 21:50 ` Dan Magenheimer
2008-07-02 22:41 ` [PATCH] record max stime skew (was RE: [PATCH] strictly increasing hvm guest time) Dan Magenheimer
2008-07-03 8:03 ` Keir Fraser
2008-07-03 16:24 ` Dan Magenheimer
2008-07-03 16:35 ` Dan Magenheimer
2008-07-03 20:03 ` Dan Magenheimer
2008-07-03 23:00 ` Keir Fraser
2008-07-04 15:11 ` Dan Magenheimer
2008-07-04 15:22 ` Keir Fraser
2008-07-04 19:32 ` Dan Magenheimer
2008-07-04 19:56 ` Keir Fraser
2008-07-10 0:24 ` Dan Magenheimer
2008-07-10 7:40 ` Keir Fraser
2008-07-10 22:42 ` Xen system skew MUCH worse than tsc skew (was RE: RE: [PATCH] record max stime skew (was RE: [PATCH] strictly increasing hvm guest time)) Dan Magenheimer
2008-07-11 8:27 ` Keir Fraser
2008-07-11 20:53 ` Dan Magenheimer
2008-07-11 21:27 ` Xen system skew MUCH worse than tsc skew (was RE: RE: [PATCH] record max stime skew (was RE: [PATCH] strictly increasinghvm " Ian Pratt
2008-07-12 21:05 ` Dan Magenheimer
2008-07-11 21:27 ` Xen system skew MUCH worse than tsc skew (was RE: RE: [PATCH] record max stime skew (was RE: [PATCH] strictly increasing hvm " Keir Fraser
2008-07-12 21:07 ` Dan Magenheimer
2008-07-19 17:51 ` Dan Magenheimer
2008-07-21 8:32 ` Keir Fraser
2008-07-22 22:27 ` Dan Magenheimer
2008-07-22 23:07 ` Xen system skew MUCH worse than tsc skew (was RE: RE: [PATCH] record max stime skew (was RE: [PATCH] strictly increasinghvm " Ian Pratt
2008-07-23 0:40 ` Dan Magenheimer
2008-07-23 1:16 ` Ian Pratt
2008-07-23 6:11 ` Tian, Kevin
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