FreeBSD: set cpu_freq to zero if cannot read value

[PATCH] FreeBSD: set cpu_freq to zero if cannot read value

Posted by Tiago Espinha Gasiba 3 weeks ago

From: Tiago Gasiba <tiago.gasiba@gmail.com>

From: Tiago Gasiba <tiga@FreeBSD.org>

Signed-off-by: Tiago Espinha Gasiba <tiago.gasiba@gmail.com>
---
 src/util/virhostcpu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/util/virhostcpu.c b/src/util/virhostcpu.c
index f2b25e940b..b602592fb7 100644
--- a/src/util/virhostcpu.c
+++ b/src/util/virhostcpu.c
@@ -993,8 +993,8 @@ virHostCPUGetInfo(virArch hostarch G_GNUC_UNUSED,
 
     if (sysctlbyname("dev.cpu.0.freq", &cpu_freq, &cpu_freq_len, NULL, 0) < 0) {
         if (sysctlbyname("hw.clockrate", &cpu_freq, &cpu_freq_len, NULL, 0) < 0) {
-            virReportSystemError(errno, "%s", _("cannot obtain CPU freq"));
-            return -1;
+            VIR_WARN("cannot obtain CPU freq, setting to 0");
+            cpu_freq = 0;
         }
     }
 
-- 
2.50.1 (Apple Git-155)

Re: [PATCH] FreeBSD: set cpu_freq to zero if cannot read value

Posted by Roman Bogorodskiy 5 days, 18 hours ago

  Tiago Espinha Gasiba wrote:

> From: Tiago Gasiba <tiago.gasiba@gmail.com>
> 
> From: Tiago Gasiba <tiga@FreeBSD.org>
> 
> Signed-off-by: Tiago Espinha Gasiba <tiago.gasiba@gmail.com>
> ---
>  src/util/virhostcpu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/util/virhostcpu.c b/src/util/virhostcpu.c
> index f2b25e940b..b602592fb7 100644
> --- a/src/util/virhostcpu.c
> +++ b/src/util/virhostcpu.c
> @@ -993,8 +993,8 @@ virHostCPUGetInfo(virArch hostarch G_GNUC_UNUSED,
>  
>      if (sysctlbyname("dev.cpu.0.freq", &cpu_freq, &cpu_freq_len, NULL, 0) < 0) {
>          if (sysctlbyname("hw.clockrate", &cpu_freq, &cpu_freq_len, NULL, 0) < 0) {
> -            virReportSystemError(errno, "%s", _("cannot obtain CPU freq"));
> -            return -1;
> +            VIR_WARN("cannot obtain CPU freq, setting to 0");
> +            cpu_freq = 0;
>          }
>      }
>  

Merge request provides more details on this issue:
https://gitlab.com/libvirt/libvirt/-/merge_requests/553.

Apparently, calling virReportSystemError() from virHostCPUGetInfo() is
not desired. This function is used by drivers to implement
virNodeGetInfo(), so raising error here prevents from using the
virNodeGetInfo() API. This leads to other issues, e.g. virt-manager
fails to connect to the driver if virNodeGetInfo() errors out.

Falling back to CPU frequency 0 if it cannot be obtained looks like a
sane option. In theory, it could cause division by 0, but in practice it
does not seem that cpu frequency could be used as a divisor.

virt-manager does not seem to actually use CPU frequency it gets from
virNodeGetInfo(). And virsh prints out CPU frequency only if it is not
zero.

Having that said:

Reviewed-by: Roman Bogorodskiy <bogorodskiy@gmail.com>

I'll wait a few days before pushing in case if anyone has objects to
this fallback behavior.

Re: [PATCH] FreeBSD: set cpu_freq to zero if cannot read value

Posted by Daniel P. Berrangé via Devel 5 days, 18 hours ago

On Wed, Aug 12, 2026 at 10:36:51AM +0200, Roman Bogorodskiy wrote:
>   Tiago Espinha Gasiba wrote:
> 
> > From: Tiago Gasiba <tiago.gasiba@gmail.com>
> > 
> > From: Tiago Gasiba <tiga@FreeBSD.org>
> > 
> > Signed-off-by: Tiago Espinha Gasiba <tiago.gasiba@gmail.com>
> > ---
> >  src/util/virhostcpu.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/src/util/virhostcpu.c b/src/util/virhostcpu.c
> > index f2b25e940b..b602592fb7 100644
> > --- a/src/util/virhostcpu.c
> > +++ b/src/util/virhostcpu.c
> > @@ -993,8 +993,8 @@ virHostCPUGetInfo(virArch hostarch G_GNUC_UNUSED,
> >  
> >      if (sysctlbyname("dev.cpu.0.freq", &cpu_freq, &cpu_freq_len, NULL, 0) < 0) {
> >          if (sysctlbyname("hw.clockrate", &cpu_freq, &cpu_freq_len, NULL, 0) < 0) {
> > -            virReportSystemError(errno, "%s", _("cannot obtain CPU freq"));
> > -            return -1;
> > +            VIR_WARN("cannot obtain CPU freq, setting to 0");
> > +            cpu_freq = 0;
> >          }
> >      }
> >  
> 
> Merge request provides more details on this issue:
> https://gitlab.com/libvirt/libvirt/-/merge_requests/553.
> 
> Apparently, calling virReportSystemError() from virHostCPUGetInfo() is
> not desired. This function is used by drivers to implement
> virNodeGetInfo(), so raising error here prevents from using the
> virNodeGetInfo() API. This leads to other issues, e.g. virt-manager
> fails to connect to the driver if virNodeGetInfo() errors out.
> 
> Falling back to CPU frequency 0 if it cannot be obtained looks like a
> sane option. In theory, it could cause division by 0, but in practice it
> does not seem that cpu frequency could be used as a divisor.
> 
> virt-manager does not seem to actually use CPU frequency it gets from
> virNodeGetInfo(). And virsh prints out CPU frequency only if it is not
> zero.
> 
> Having that said:
> 
> Reviewed-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
> 
> I'll wait a few days before pushing in case if anyone has objects to
> this fallback behavior.

Fine to push, but just downgrade the log message to VIR_DEBUG.  We don't
want to use VIR_WARN in scenarios which are "expected behaviour" as that
pollutes logs for users who have that (otherwise acceptable) deployment
scenario.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

With regards,
Daniel
-- 
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Re: [PATCH] FreeBSD: set cpu_freq to zero if cannot read value

Posted by decidefunding--- via Devel 5 days, 16 hours ago

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