Commit ac66a73b authored by H. Peter Anvin's avatar H. Peter Anvin Committed by Borislav Petkov (AMD)
Browse files

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: default avatarH. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: default avatarSohil Mehta <sohil.mehta@intel.com>
Link: https://patch.msgid.link/20260325230151.1898287-2-hpa@zytor.com
parent c3692998

Documentation/admin-guide/kernel-parameters.txt

+2 −2
Original line number Diff line number Diff line
@@ -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

arch/x86/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -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.

arch/x86/kernel/cpu/common.c

+1 −1
Original line number Diff line number Diff line
@@ -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));