Re: [Xen-devel] [PATCH] xen/domctl: lower loglevel of XEN_DOMCTL_memory_mapping

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Sep 09, 2015 at 02:50:25PM +0800, Tiejun Chen wrote:
> We should lower loglevel to XENLOG_G_DEBUG while mapping or
> unmapping memory via XEN_DOMCTL_memory_mapping since its
> fair enough to check this info just while debugging.

The issue you folks are hitting where it takes eons to boot
with a large BAR _may_ be related to tasklets and triggering
the hypercall_preempt_check().

I think you may be using 'console_to_ring' or such and collecting
the hypervisor logs. That will schedule an tasklet whenever printk
is used - and the tasklet will cause hypercall_preempt_check() to
return true.

So what we get is that on the entrace (even before calling map_mmio_region)
for this function we have an outstanding softirq we must process - which
means that this function exits as soon as possible to service it.

Perhaps the solution is remove the first printk(s) and just have them
once the operation has completed? That may fix the outstanding tasklet
problem?

Could you try that (or perhaps you have already tried it?) please?

> 
> CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
> CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Keir Fraser <keir@xxxxxxx>
> CC: Tim Deegan <tim@xxxxxxx>
> Signed-off-by: Tiejun Chen <tiejun.chen@xxxxxxxxx>
> ---
>  xen/common/domctl.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/common/domctl.c b/xen/common/domctl.c
> index 7f959f3..3bf39f1 100644
> --- a/xen/common/domctl.c
> +++ b/xen/common/domctl.c
> @@ -1049,7 +1049,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
> u_domctl)
>  
>          if ( add )
>          {
> -            printk(XENLOG_G_INFO
> +            printk(XENLOG_G_DEBUG
>                     "memory_map:add: dom%d gfn=%lx mfn=%lx nr=%lx\n",
>                     d->domain_id, gfn, mfn, nr_mfns);
>  
> @@ -1061,7 +1061,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
> u_domctl)
>          }
>          else
>          {
> -            printk(XENLOG_G_INFO
> +            printk(XENLOG_G_DEBUG
>                     "memory_map:remove: dom%d gfn=%lx mfn=%lx nr=%lx\n",
>                     d->domain_id, gfn, mfn, nr_mfns);
>  
> -- 
> 1.9.1
> 
> 
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