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Re: [PATCH] x86/time: make do_settime() uses more accurate
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 7 May 2026 12:26:51 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
- Delivery-date: Thu, 07 May 2026 10:27:09 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Wed, May 06, 2026 at 11:35:45AM +0200, Jan Beulich wrote:
> As a comment next to one of the invocations states, get_wallclock_time()
> can take over a second. The order of evaluation of function arguments is
> in principle unspecified; in practice at least gcc looks to be evaluating
> them from last to first. Hence with NOW() invoked first, the respective
> value passed to do_settime() can be off by over a second (which is in
> contrast to __get_cmos_time() attempting to get the time exactly after an
> update, i.e. [pretty] precisely at a seconds boundary).
>
> This also addresses a Misra C:2012 rule 13.2 ("The value of an expression
> and its persistent side-effects shall be the same under all permitted
> evaluation orders") violation each.
>
> Fixes: f64134cdb81c ("x86: Fix time_resume() to notify all domains of
> wallclock change")
> Fixes: 0bfcf984b727 ("x86: Reintroduce clocksource=tsc")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Thanks, Roger.
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