linux-kernel - Re: [PATCH 1/1] turbostat: cpu9: msr offset 0x614 read failed: Input/output error

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Date:   Thu, 25 Aug 2022 13:38:23 -0700
From:   samasth.norway.ananda@...cle.com
To:     linux-pm@...r.kernel.org
Cc:     lenb@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] turbostat: cpu9: msr offset 0x614 read failed:
 Input/output error



On 1/24/22 10:04 AM, samasth.norway.ananda wrote:
> I get the following error running Turbostat on an intel virtual machine.
> 
> turbostat.5.4.17-2136.300.7.el7uek.x86_64: cpu49: msr offset 0x614 read
> failed: Input/output error
> 
> The below patch gives a more user friendly message. It is based on the
> patch for turbostat from Prarit Bhargava that was posted some time ago.
> The patch is "[v2] turbostat: Running on virtual machine is not supported" [1]
> and also similar to the patch for x86_energy_perf_policy posted by Ondřej Lysoněk.
> The patch is “tools/power x86_energy_perf_policy: Input/output error in a VM"[2].
> 
> KVM disables MONITOR/MWAIT in __do_cpuid_func(). Hence no VM will have MWAIT
> and hence turbostat will not be able to read any C-state related registers
> like the failures we see when we run turbostat. Therefore, turbostat should
> also gracefully error-out like x86_energy_perf_policy.c.
> 
> [1] https://patchwork.kernel.org/patch/9868587/
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0936cdfbb527
> 
> Signed-off-by: Samasth Norway Ananda <samasth.norway.ananda@...cle.com>
> ---
>   tools/power/x86/turbostat/turbostat.c | 68 ++++++++++++++++++++++-----
>   1 file changed, 55 insertions(+), 13 deletions(-)
> 
> diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
> index 47d3ba895d6d..c2904c1c0830 100644
> --- a/tools/power/x86/turbostat/turbostat.c
> +++ b/tools/power/x86/turbostat/turbostat.c
> @@ -538,14 +538,68 @@ int get_instr_count_fd(int cpu)
>   	return fd_instr_count_percpu[cpu];
>   }
>   
> +/*
> + *  * Open a file, and exit on failure
> + *   */
> +FILE *fopen_or_die(const char *path, const char *mode)
> +{
> +        FILE *filep = fopen(path, mode);
> +
> +        if (!filep)
> +                err(1, "%s: open failed", path);
> +        return filep;
> +}
> +
> +void err_on_hypervisor(void)
> +{
> +	FILE *cpuinfo;
> +	char *flags, *hypervisor;
> +	char *buffer;
> +
> +	/* On VMs /proc/cpuinfo contains a "flags" entry for hypervisor */
> +	cpuinfo = fopen_or_die("/proc/cpuinfo", "ro");
> +
> +	buffer = malloc(4096);
> +	if (!buffer) {
> +		fclose(cpuinfo);
> +		err(-ENOMEM, "buffer malloc fail");
> +	}
> +
> +	if (!fread(buffer, 1024, 1, cpuinfo)) {
> +		fclose(cpuinfo);
> +		free(buffer);
> +		err(1, "Reading /proc/cpuinfo failed");
> +	}
> +
> +	flags = strstr(buffer, "flags");
> +	rewind(cpuinfo);
> +	fseek(cpuinfo, flags - buffer, SEEK_SET);
> +	if (!fgets(buffer, 4096, cpuinfo)) {
> +		fclose(cpuinfo);
> +		free(buffer);
> +		err(1, "Reading /proc/cpuinfo failed");
> +	}
> +	fclose(cpuinfo);
> +
> +	hypervisor = strstr(buffer, "hypervisor");
> +
> +	free(buffer);
> +
> +	if (hypervisor)
> +		err(-1,
> +		    "not supported on this virtual machine");
> +}
> +
>   int get_msr(int cpu, off_t offset, unsigned long long *msr)
>   {
>   	ssize_t retval;
>   
>   	retval = pread(get_msr_fd(cpu), msr, sizeof(*msr), offset);
>   
> -	if (retval != sizeof *msr)
> +	if (retval != sizeof *msr){
> +		err_on_hypervisor();
>   		err(-1, "cpu%d: msr offset 0x%llx read failed", cpu, (unsigned long long)offset);
> +	}
>   
>   	return 0;
>   }
> @@ -1858,18 +1912,6 @@ static unsigned long long rdtsc(void)
>   	return low | ((unsigned long long)high) << 32;
>   }
>   
> -/*
> - * Open a file, and exit on failure
> - */
> -FILE *fopen_or_die(const char *path, const char *mode)
> -{
> -	FILE *filep = fopen(path, mode);
> -
> -	if (!filep)
> -		err(1, "%s: open failed", path);
> -	return filep;
> -}
> -
>   /*
>    * snapshot_sysfs_counter()
>    *
A gentle reminder, I haven't received any response on this. Any 
comments/feedback/concern?

Thanks,
Samasth.
Oracle Linux Team.