Re: port-amd64/47967: DTrace does not work while running under QEMU

[christos%zoulas.com@localhost (Christos Zoulas)]

The following reply was made to PR port-amd64/47967; it has been noted by GNATS.

From: christos%zoulas.com@localhost (Christos Zoulas)
To: gnats-bugs%NetBSD.org@localhost, 
port-amd64-maintainer%netbsd.org@localhost, 
        gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost, 
riz%NetBSD.org@localhost
Cc: 
Subject: Re: port-amd64/47967: DTrace does not work while running under QEMU
Date: Wed, 26 Jun 2013 18:28:08 -0400

 On Jun 26,  9:20pm, david%l8s.co.uk@localhost (David Laight) wrote:
 -- Subject: Re: port-amd64/47967: DTrace does not work while running under QE
 
 |  Surely it would be much better to probe for the symptom, rather
 |  than a random string.
 
 Ok, how about:
 
 Index: identcpu.c
 ===================================================================
 RCS file: /cvsroot/src/sys/arch/x86/x86/identcpu.c,v
 retrieving revision 1.33
 diff -u -p -u -r1.33 identcpu.c
 --- identcpu.c 26 Jun 2013 20:52:28 -0000      1.33
 +++ identcpu.c 26 Jun 2013 22:19:26 -0000
 @@ -58,6 +58,7 @@ static const struct x86_cache_info amd_c
        AMD_L3CACHE_INFO;
  
  int cpu_vendor;
 +int cpu_msr_tsc;
  char cpu_brand_string[49];
  
  /*
 @@ -563,14 +564,17 @@ cpu_probe_geode(struct cpu_info *ci)
  }
  
  static void
 -cpu_probe_qemu(struct cpu_info *ci)
 +cpu_probe_msr_tsc(struct cpu_info *ci)
  {
 -       if (memcmp("QEMU Virtual CPU", cpu_brand_string, 16) != 0)
 -               return;
 +      cpu_msr_tsc = (cpu_feature[0] & CPUID_MSR) != 0;
 +      if (!cpu_msr_tsc)
 +              return;
 +
 +      if (rdmsr(MSR_TSC) != 0)
 +              return;
  
 -       /* if QEMU does not implement MSR_TSC, disable the TSC */
 -       ci->ci_feat_val[0] &= ~CPUID_MSR;
 -       cpu_feature[0] &= ~CPUID_MSR;
 +      aprint_error_dev(ci->ci_dev, "Bad MSR_TSC support");
 +      cpu_msr_tsc = 0;
  }
  
  static void
 @@ -720,7 +724,7 @@ cpu_probe(struct cpu_info *ci)
        cpu_probe_c3(ci);
        cpu_probe_geode(ci);
        cpu_probe_vortex86(ci);
 -      cpu_probe_qemu(ci);
 +      cpu_probe_msr_tsc(ci);
  
        x86_cpu_topology(ci);
  
 Index: tsc.c
 ===================================================================
 RCS file: /cvsroot/src/sys/arch/x86/x86/tsc.c,v
 retrieving revision 1.30
 diff -u -p -u -r1.30 tsc.c
 --- tsc.c      8 Aug 2011 17:00:23 -0000       1.30
 +++ tsc.c      26 Jun 2013 22:19:26 -0000
 @@ -258,10 +258,12 @@ cpu_hascounter(void)
        return cpu_feature[0] & CPUID_TSC;
  }
  
 +extern int cpu_msr_tsc;
 +
  uint64_t
  cpu_counter_serializing(void)
  {
 -      if (cpu_feature[0] & CPUID_MSR)
 +      if (cpu_msr_tsc)
                return rdmsr(MSR_TSC);
        else
                return cpu_counter();