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From: Dario Faggioli <dario.faggioli@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
	Jan Beulich <JBeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>
Cc: Joao Martins <joao.m.martins@oracle.com>
Subject: Re: [PATCH 3/8] x86/time: introduce and use rdtsc_ordered()
Date: Mon, 11 Jul 2016 13:39:24 +0200	[thread overview]
Message-ID: <1468237164.13039.4.camel@citrix.com> (raw)
In-Reply-To: <206387df-d279-d23c-b796-4e124acaf1da@citrix.com>


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On Mon, 2016-06-20 at 13:59 +0100, Andrew Cooper wrote:
> On 15/06/16 11:27, Jan Beulich wrote:
> > Matching Linux commit 03b9730b76 ("x86/asm/tsc: Add rdtsc_ordered()
> > and
> > use it in trivial call sites") and earlier ones it builds upon,
> > let's
> > make sure timing loops don't have their rdtsc()-s re-ordered, as
> > that
> > would harm precision of the result (values were observed to be
> > several
> > hundred clocks off without this adjustment).
> > 
> > Signed-off-by: Jan Beulich <jbeulich@suse.com>
>  
> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
>
FWIW:

Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Tested-by: Dario Faggioli <dario.faggioli@citrix.com>

(or Reviewed-and-Tested-by: as you wish :-)).

FTR, during my own investigation, before raising the issue on the
mailing list, I also came to the conclusion that we'd need something
like this. I even try doing something like this (in a much more hacky
way), and had the feeling that it was making a difference but, of
course, alone, without all the other issues that Jan found and fixed in
this series, it wasn't enough.

Thanks and regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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  parent reply	other threads:[~2016-07-11 11:39 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-15  9:50 [PATCH 0/8] x86/time: improve cross-CPU clock monotonicity (and more) Jan Beulich
2016-06-15 10:26 ` [PATCH 1/8] " Jan Beulich
2016-06-15 10:32   ` Jan Beulich
2016-06-15 22:51   ` Joao Martins
2016-06-16  8:27     ` Jan Beulich
2016-06-16 20:27       ` Joao Martins
2016-06-17  7:32         ` Jan Beulich
2016-06-21 12:05           ` Joao Martins
2016-06-21 12:28             ` Jan Beulich
2016-06-21 13:57               ` Joao Martins
2016-08-02 19:30   ` Andrew Cooper
2016-06-15 10:26 ` [PATCH 2/8] x86: also generate assembler usable equates for synthesized features Jan Beulich
2016-06-20 12:50   ` Andrew Cooper
2016-06-15 10:27 ` [PATCH 3/8] x86/time: introduce and use rdtsc_ordered() Jan Beulich
2016-06-20 12:59   ` Andrew Cooper
2016-06-20 13:06     ` Jan Beulich
2016-06-20 13:07       ` Andrew Cooper
2016-07-11 11:39     ` Dario Faggioli [this message]
2016-06-15 10:28 ` [PATCH 4/8] x86/time: calibrate TSC against platform timer Jan Beulich
2016-06-20 14:20   ` Andrew Cooper
2016-06-20 15:19     ` Jan Beulich
2016-08-02 19:25       ` Andrew Cooper
2016-08-03  9:32         ` Jan Beulich
2016-06-15 10:28 ` [PATCH 5/8] x86/time: correctly honor late clearing of TSC related feature flags Jan Beulich
2016-06-20 14:32   ` Andrew Cooper
2016-06-20 15:20     ` Jan Beulich
2016-07-04 15:39       ` Andrew Cooper
2016-07-04 15:53         ` Jan Beulich
2016-08-02 19:08           ` Andrew Cooper
2016-08-03  9:43             ` Jan Beulich
2016-08-31 13:42               ` Andrew Cooper
2016-08-31 14:03                 ` Jan Beulich
2016-06-15 10:29 ` [PATCH 6/8] x86/time: support 32-bit wide ACPI PM timer Jan Beulich
2016-07-04 15:40   ` Andrew Cooper
2016-06-15 10:30 ` [PATCH 7/8] x86/time: fold recurring code Jan Beulich
2016-07-04 15:43   ` Andrew Cooper
2016-06-15 10:30 ` [PATCH 8/8] x86/time: group time stamps into a structure Jan Beulich
2016-07-04 15:57   ` Andrew Cooper
2016-07-01  7:44 ` Ping: [PATCH 0/8] x86/time: improve cross-CPU clock monotonicity (and more) Jan Beulich

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