From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Krister Johansen <kjlx@templeofstupid.com>,
Juergen Gross <jgross@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
Marcelo Tosatti <mtosatti@redhat.com>,
Anthony Liguori <aliguori@amazon.com>,
David Reaver <me@davidreaver.com>,
Brendan Gregg <brendan@intel.com>
Subject: Re: [PATCH linux-next v2] x86/xen/time: prefer tsc as clocksource when it is invariant
Date: Mon, 12 Dec 2022 13:48:24 -0500 [thread overview]
Message-ID: <d1a2b785-edc7-b7da-d2f2-123d1555022e@oracle.com> (raw)
In-Reply-To: <20221212160524.GB1973@templeofstupid.com>
On 12/12/22 11:05 AM, Krister Johansen wrote:
>
> diff --git a/arch/x86/include/asm/xen/cpuid.h b/arch/x86/include/asm/xen/cpuid.h
> index 6daa9b0c8d11..d9d7432481e9 100644
> --- a/arch/x86/include/asm/xen/cpuid.h
> +++ b/arch/x86/include/asm/xen/cpuid.h
> @@ -88,6 +88,12 @@
> * EDX: shift amount for tsc->ns conversion
> * Sub-leaf 2: EAX: host tsc frequency in kHz
> */
> +#define XEN_CPUID_TSC_EMULATED (1u << 0)
> +#define XEN_CPUID_HOST_TSC_RELIABLE (1u << 1)
> +#define XEN_CPUID_RDTSCP_INSTR_AVAIL (1u << 2)
> +#define XEN_CPUID_TSC_MODE_DEFAULT (0)
> +#define XEN_CPUID_TSC_MODE_EMULATE (1u)
> +#define XEN_CPUID_TSC_MODE_NOEMULATE (2u)
This file is a copy of Xen public interface so this change should go to Xen first.
>
> +static int __init xen_tsc_safe_clocksource(void)
> +{
> + u32 eax, ebx, ecx, edx;
> +
> + if (!(xen_hvm_domain() || xen_pvh_domain()))
> + return 0;
> +
> + if (!(boot_cpu_has(X86_FEATURE_CONSTANT_TSC)))
> + return 0;
> +
> + if (!(boot_cpu_has(X86_FEATURE_NONSTOP_TSC)))
> + return 0;
> +
> + if (check_tsc_unstable())
> + return 0;
> +
> + cpuid(xen_cpuid_base() + 3, &eax, &ebx, &ecx, &edx);
> +
> + if (eax & XEN_CPUID_TSC_EMULATED)
> + return 0;
> +
> + if (ebx != XEN_CPUID_TSC_MODE_NOEMULATE)
> + return 0;
Why is the last test needed?
-boris
next prev parent reply other threads:[~2022-12-12 18:52 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-08 16:36 [PATCH linux-next] x86/xen/time: prefer tsc as clocksource when it is invariant Krister Johansen
2022-12-09 19:32 ` Boris Ostrovsky
2022-12-12 15:57 ` Krister Johansen
2022-12-12 16:05 ` [PATCH linux-next v2] " Krister Johansen
2022-12-12 16:46 ` Jan Beulich
2022-12-12 22:05 ` Krister Johansen
2022-12-13 7:23 ` Jan Beulich
2022-12-13 18:58 ` Krister Johansen
2022-12-14 8:17 ` Jan Beulich
2022-12-14 18:01 ` Krister Johansen
2022-12-12 18:48 ` Boris Ostrovsky [this message]
2022-12-12 22:09 ` Krister Johansen
2022-12-13 21:25 ` Boris Ostrovsky
2022-12-14 18:01 ` Krister Johansen
2022-12-14 21:46 ` Boris Ostrovsky
2022-12-16 16:20 ` Krister Johansen
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