From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Keir Fraser <keir@xen.org>, Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH] x86: Adjust rdtsc inline assembly
Date: Wed, 18 Feb 2015 13:59:08 +0000 [thread overview]
Message-ID: <54E49AAC.7010407@citrix.com> (raw)
In-Reply-To: <54E49D99020000780006114E@mail.emea.novell.com>
On 18/02/15 13:11, Jan Beulich wrote:
>>>> On 18.02.15 at 13:25, <andrew.cooper3@citrix.com> wrote:
>> The single use of the old rdtsc() in emulate_privileged_op() is altered to use
>> the new rdtsc() and the rdmsr_writeback path to set eax/edx appropriately.
> I'm not entirely sure about this one - the current code surely is slightly
> faster than the replacement. Question is how much this matters. I'd
> suggest to be on the safe side and simply open-code the asm() there.
It is a matter of a 4 instructions on a fault slowpath, which which only
ever executed in the unlikely case that vtsc is enabled on a domain, or
the kernel has set CR4.TSD.
I would not loose sleep over the introduced inefficiently.
~Andrew
next prev parent reply other threads:[~2015-02-18 13:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-18 12:25 [PATCH] x86: Adjust rdtsc inline assembly Andrew Cooper
2015-02-18 13:11 ` Jan Beulich
2015-02-18 13:59 ` Andrew Cooper [this message]
2015-02-18 14:05 ` [PATCH v2] " Andrew Cooper
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