Re: [Xen-devel] Question to Xen log level in the case of PT

[Chen, Tiejun]

So can Xen change log level dynamically like Linux? If yes, we might
change this level temporarily while passing through IGD. If not, any
suggestion?


First of all you could boot without lowering the log level (non-debug
builds) or raising the log level ("loglvl=warning"; debug builds). But


Sorry I don't know how to build "non-debug" here. Could you give me this 
detail? Or where I can get this info?



that would change the log level for the entire session, which may
not be what you're after. I too realized that having a way to
dynamically adjust the log level would be useful occasionally. For
post-4.6 I have a patch (attached) ready allowing to do so in a
limited way from the serial console (and hence also via "xl debug-key").
As you'll see in there I also took note of it probably being desirable
to have a sysctl (and then a wrapping xl command) to full control the
log level. I didn't get around to implement that yet.


Good to know this.



Otoh the specific messages you cite are of quite questionable use
in the first place. I certainly would welcome a patch lowering their
priority to XENLOG_G_DEBUG (which however would still not


Done.

Thanks
Tiejun



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Re: [Xen-devel] Question to Xen log level in the case of PT

[Jan Beulich]

>>> On 09.09.15 at 08:53,  wrote:
>> > So can Xen change log level dynamically like Linux? If yes, we might
>>> change this level temporarily while passing through IGD. If not, any
>>> suggestion?
>>
>> First of all you could boot without lowering the log level (non-debug
>> builds) or raising the log level ("loglvl=warning"; debug builds). But
> 
> Sorry I don't know how to build "non-debug" here. Could you give me this 
> detail? Or where I can get this info?

Config.mk has

# A debug build of Xen and tools?
debug ?= y
debug_symbols ?= $(debug)

which you can alter or override on the make command line or in
.config. But for development purposes you really want to build
debug mode binaries, and rather adjust the log level on the
command line.

Jan


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[Xen-devel] Question to Xen log level in the case of PT

[Chen, Tiejun]

All guys,

Sorry to raise a question to you since I'm not very sure how to deal 
with this.


When I passthrough a device like IGD, I can see so many messages:

"memory_map:add:" and "memory_map:remove:"

since we have to add/remove all pages map residing PCI bar. Especially 
as a graphic device, oftentimes this range would occupy dozens of MB, 
even hundreds of MB. These print messages consume a lot of time to boot 
a VM. For instance, it takes about 5 minutes to boot a Windows guest on 
my BDW. But if I remove these output simply like this,


diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 7f959f3..82da9d1 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -1049,10 +1049,6 @@ long 
do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)


 if ( add )
 {
-printk(XENLOG_G_INFO
-   "memory_map:add: dom%d gfn=%lx mfn=%lx nr=%lx\n",
-   d->domain_id, gfn, mfn, nr_mfns);
-
 ret = map_mmio_regions(d, gfn, nr_mfns, mfn);
 if ( ret )
 printk(XENLOG_G_WARNING
@@ -1061,10 +1057,6 @@ long 
do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)

 }
 else
 {
-printk(XENLOG_G_INFO
-   "memory_map:remove: dom%d gfn=%lx mfn=%lx nr=%lx\n",
-   d->domain_id, gfn, mfn, nr_mfns);
-
 ret = unmap_mmio_regions(d, gfn, nr_mfns, mfn);
 if ( ret && is_hardware_domain(current->domain) )
 printk(XENLOG_ERR

its down to a half, about 2.5 minutes.

I know I can't delete this directly. But currently there are four log 
level on Xen side,


 *   XENLOG_ERR: Fatal errors, either Xen, Guest or Dom0
 *   is about to crash.
 *
 *   XENLOG_WARNING: Something bad happened, but we can recover.
 *
 *   XENLOG_INFO: Interesting stuff, but not too noisy.
 *
 *   XENLOG_DEBUG: Use where ever you like. Lots of noise.

looks I have to change XENLOG_G_INFO to XENLOG_G_WARNING but its not 
appropriate here.


So can Xen change log level dynamically like Linux? If yes, we might 
change this level temporarily while passing through IGD. If not, any 
suggestion?


Thanks
Tiejun

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