From ac66a73be03a0a72aeeb33d3610cfc43cb101a0b Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Wed, 25 Mar 2026 16:01:47 -0700 Subject: [PATCH] x86/fred: Enable FRED by default When FRED was added to the mainline kernel, it was set up as an explicit opt-in due to the risk of regressions before hardware was available publicly. Now, Panther Lake (Core Ultra 300 series) has been released, and benchmarking by Phoronix has shown that it provides a significant performance benefit on most workloads: https://www.phoronix.com/review/intel-fred-panther-lake Accordingly, enable FRED by default if the CPU supports it. FRED can of course still be disabled via the fred=off command line option. Touch up Kconfig help too. Signed-off-by: H. Peter Anvin (Intel) Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Sohil Mehta Link: https://patch.msgid.link/20260325230151.1898287-2-hpa@zytor.com --- Documentation/admin-guide/kernel-parameters.txt | 4 ++-- arch/x86/Kconfig | 2 +- arch/x86/kernel/cpu/common.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 03a550630644..bfa8a20ccc37 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1750,8 +1750,8 @@ Kernel parameters fred= [X86-64] Enable/disable Flexible Return and Event Delivery. Format: { on | off } - on: enable FRED when it's present. - off: disable FRED, the default setting. + on: enable FRED when it's present, the default setting. + off: disable FRED. ftrace=[tracer] [FTRACE] will set and start the specified tracer diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index e2df1b147184..876b663dcf38 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -557,7 +557,7 @@ config X86_FRED bool "Flexible Return and Event Delivery" depends on X86_64 help - When enabled, try to use Flexible Return and Event Delivery + When enabled, use Flexible Return and Event Delivery instead of the legacy SYSCALL/SYSENTER/IDT architecture for ring transitions and exception/interrupt handling if the system supports it. diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index a8ff4376c286..0b02cb038d7f 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1746,7 +1746,7 @@ static void __init cpu_parse_early_param(void) /* Minimize the gap between FRED is available and available but disabled. */ arglen = cmdline_find_option(boot_command_line, "fred", arg, sizeof(arg)); - if (arglen != 2 || strncmp(arg, "on", 2)) + if (arglen == 3 && !strncmp(arg, "off", 3)) setup_clear_cpu_cap(X86_FEATURE_FRED); arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));