linux-kernel - VDSO and Intel Skylake Virtualization

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Message-ID: <fcedc2b3-f36e-b0eb-43f1-cfa244ca2409@exegy.com>
Date:   Wed, 8 Nov 2017 10:11:55 -0600
From:   "Mr. Berkley Shands" <bshands@...gy.com>
To:     linux-kernel <linux-kernel@...r.kernel.org>
Subject: VDSO and Intel Skylake Virtualization

FYI: We discovered the clock_gettime(CLOCK_REALTIME, &ts); was taking >
6900 cycles to run
on intel skylake cpus. Normal is ~60 cycles. In the kernel vdso code is
a very nice comment about 1:1
paring in the hypervisor or the syscall would be eventually used.
Sorry, but with no hypervisor running, the vdso call will always time
out and call the syscall.
Disabling the Intel Virtualization in the BIOS corrects this issue, and
the clock_gettime() runs as it should.
It appears that many folks have run into this issue, and are looking for
a solution.
Should the kernel check to see if there is a hypervisor before getting
confused in __vdso_clock_gettime() ?

Berkley

--

//E. F. Berkley Shands, MSc
Senior Software Architect/Engineer
Exegy Systems Engineering//

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