From: Ingo Molnar <mingo@kernel.org>
To: Joerg Roedel <jroedel@suse.de>
Cc: Shaohua Li <shli@fb.com>,
linux-kernel@vger.kernel.org, gang.wei@intel.com,
hpa@linux.intel.com, kernel-team@fb.com, ning.sun@intel.com,
srihan@fb.com, alex.eydelberg@intel.com
Subject: Re: [PATCH V2] x86/tboot: add an option to disable iommu force on
Date: Thu, 27 Apr 2017 08:52:53 +0200 [thread overview]
Message-ID: <20170427065253.zuq4a43girwcsotu@gmail.com> (raw)
In-Reply-To: <20170426215936.GT5077@suse.de>
* Joerg Roedel <jroedel@suse.de> wrote:
> On Wed, Apr 26, 2017 at 09:18:35AM -0700, Shaohua Li wrote:
> > IOMMU harms performance signficantly when we run very fast networking
> > workloads. It's 40GB networking doing XDP test. Software overhead is
> > almost unaware, but it's the IOTLB miss (based on our analysis) which
> > kills the performance. We observed the same performance issue even with
> > software passthrough (identity mapping), only the hardware passthrough
> > survives. The pps with iommu (with software passthrough) is only about
> > ~30% of that without it. This is a limitation in hardware based on our
> > observation, so we'd like to disable the IOMMU force on, but we do want
> > to use TBOOT and we can sacrifice the DMA security bought by IOMMU. I
> > must admit I know nothing about TBOOT, but TBOOT guys (cc-ed) think not
> > eabling IOMMU is totally ok.
> >
> > So introduce a new boot option to disable the force on. It's kind of
> > silly we need to run into intel_iommu_init even without force on, but we
> > need to disable TBOOT PMR registers. For system without the boot option,
> > nothing is changed.
> >
> > Signed-off-by: Shaohua Li <shli@fb.com>
>
> Applied, thanks.
Please don't apply it yet, I posted a few review questions.
Thanks,
Ingo
next prev parent reply other threads:[~2017-04-27 6:53 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-26 16:18 [PATCH V2] x86/tboot: add an option to disable iommu force on Shaohua Li
2017-04-26 21:59 ` Joerg Roedel
2017-04-27 6:52 ` Ingo Molnar [this message]
2017-04-28 22:07 ` Joerg Roedel
2017-04-27 6:51 ` Ingo Molnar
2017-04-27 8:42 ` Joerg Roedel
2017-04-27 14:49 ` Shaohua Li
2017-04-27 15:18 ` Joerg Roedel
2017-04-27 15:41 ` Shaohua Li
2017-04-27 16:04 ` Joerg Roedel
2017-05-05 6:59 ` Ingo Molnar
2017-05-05 8:40 ` Joerg Roedel
2017-05-06 9:48 ` Ingo Molnar
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