lkml.org 
[lkml]   [2017]   [Apr]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [RFC] x86/tboot: add an option to disable iommu force on
    On Fri, Apr 07, 2017 at 09:49:52PM +0000, Sun, Ning wrote:
    > Hi Shaohua,
    >
    > One question, did you still see the network performance penalty when Linux kernel cmdline intel_iommu was set to off ( intel_iommu=off) ?

    the boot parameter has no effect, it runs very early and set dmar_disable=1.
    The tboot code (tboot_force_iommu) runs later and force dmar_disabled = 0.

    Thanks,
    Shaohua

    > Thanks,
    > -ning
    >
    > -----Original Message-----
    > From: Joerg Roedel [mailto:jroedel@suse.de]
    > Sent: Friday, April 07, 2017 3:09 AM
    > To: Shaohua Li <shli@fb.com>
    > Cc: linux-kernel@vger.kernel.org; Wei, Gang <gang.wei@intel.com>; hpa@linux.intel.com; mingo@kernel.org; kernel-team@fb.com; Sun, Ning <ning.sun@intel.com>; srihan@fb.com; Eydelberg, Alex <alex.eydelberg@intel.com>
    > Subject: Re: [RFC] x86/tboot: add an option to disable iommu force on
    >
    > On Mon, Apr 03, 2017 at 12:19:28PM -0700, Shaohua Li wrote:
    > > On Wed, Mar 22, 2017 at 07:50:55AM -0400, Shaohua Li wrote:
    > > > On Wed, Mar 22, 2017 at 11:49:00AM +0100, Joerg Roedel wrote:
    > > > > Hi Shaohua,
    > > > >
    > > > > On Tue, Mar 21, 2017 at 11:37:51AM -0700, Shaohua Li wrote:
    > > > > > IOMMU harms performance signficantly when we run very fast
    > > > > > networking workloads. 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.
    > > > >
    > > > > Can you elaborate a bit more on the setup where the IOMMU still
    > > > > harms network performance? With the recent scalability
    > > > > improvements I measured only a minimal impact on 10GBit networking.
    > > > Hi,
    > > >
    > > > 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.
    > >
    > > Any update on this?
    >
    > An explicit Ack from the tboot guys would be good to have.
    >
    >
    > Joerg
    >

    \
     
     \ /
      Last update: 2017-04-10 06:33    [W:4.653 / U:0.324 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site