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

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

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();