From 862e13f6710d6ede9ed0db66b1a866ecd7dd0028 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Thu, 26 Jul 2018 15:03:16 +0200 Subject: [PATCH 021/166] efi: Disable runtime services on RT Based on measurements the EFI functions get_variable / get_next_variable take up to 2us which looks okay. The functions get_time, set_time take around 10ms. These 10ms are too much. Even one ms would be too much. Ard mentioned that SetVariable might even trigger larger latencies if the firmware will erase flash blocks on NOR. The time-functions are used by efi-rtc and can be triggered during run-time (either via explicit read/write or ntp sync). The variable write could be used by pstore. These functions can be disabled without much of a loss. The poweroff / reboot hooks may be provided by PSCI. Disable EFI's runtime wrappers on PREEMPT_RT. This was observed on "EFI v2.60 by SoftIron Overdrive 1000". Acked-by: Ard Biesheuvel Signed-off-by: Sebastian Andrzej Siewior Link: https://lkml.kernel.org/r/20210924134919.1913476-2-bigeasy@linutronix.de --- drivers/firmware/efi/efi.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: linux-5.15.32-rt39/drivers/firmware/efi/efi.c =================================================================== --- linux-5.15.32-rt39.orig/drivers/firmware/efi/efi.c +++ linux-5.15.32-rt39/drivers/firmware/efi/efi.c @@ -66,7 +66,7 @@ struct mm_struct efi_mm = { struct workqueue_struct *efi_rts_wq; -static bool disable_runtime; +static bool disable_runtime = IS_ENABLED(CONFIG_PREEMPT_RT); static int __init setup_noefi(char *arg) { disable_runtime = true;