On 5 Oct 2020, at 20:21, Shinde, Archana M <archana.m.shinde@intel.com> wrote:
Christophe, looks like the bug you mentioned is not public yet, alteast I am not able to access it.
Sorry about that.
Agree with disabling DAX, although as Snir mentioned would like to see any upstream bugs opened to track this.
In addition, we are using a 5.6 kernel with Dax patches by default for virtiofs for both qemu-virtiofs and cloud-hypervisor. I propose we instead switch to the LTS 5.4 upstream kernel that has all the bits for virtiofs except Dax. If some user wants to use dax, they can switch to the experimental 5.6 kernel instead.
Do you know what is the failure mode if the kernel does not have DAX support and you try to configure it?
-Archana
From: Christophe de Dinechin <cdupontd@redhat.com> Date: Friday, October 2, 2020 at 2:43 AM To: "Dr. David Alan Gilbert" <dgilbert@redhat.com> Cc: kata-dev <kata-dev@lists.katacontainers.io> Subject: Re: [kata-dev] Dax enablement in 2.0
On 2 Oct 2020, at 11:24, Dr. David Alan Gilbert <dgilbert@redhat.com> wrote:
* Fabiano Fidêncio (fidencio@redhat.com) wrote:
Snir,
Firstly, let me reply to one specific bit of your email and also add a question.
[...]
IIUC it's currently enabled by default (qemu), can it be disabled? if not, is it planned to be configurable?
The current govmm codes only sets the "cache-size" when it's different from zero: https://github.com/intel/govmm/blob/master/qemu/qemu.go#L1256-L1258
So, setting virtio_fs_cache_size here https://github.com/kata-containers/kata-containers/blob/2.0-dev/src/runtime/... disables DAX.
A question I'd like to add to Snir's question is ... Wouldn't it be safer to have `virtio_fs_cache_size = 0` as a default value when using virtio-fs, at least till DAX gets solid?
I think that should work; the current qemu vhost-user-fs.c code has:
DEFINE_PROP_SIZE("cache-size", VHostUserFS, conf.cache_size, 0),
so ommitting the property should give us 0 and cache disabled and ommitting the property also means you work with upstream qemu's.
I do remember in older dev branches we had the default none-0 but finally found the error of our ways.
Do you have any idea of the timeline for the DAX issues to be resolved? 2.0 is a long-lived branch, presumably, so we want to have something in place that works when DAX is here.
You may want to look at https://bugzilla.redhat.com/show_bug.cgi?id=1876915#c30
Dave
[...]
Best Regards, -- Fabiano Fidêncio
_______________________________________________ kata-dev mailing list kata-dev@lists.katacontainers.io http://lists.katacontainers.io/cgi-bin/mailman/listinfo/kata-dev -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
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