diff options
Diffstat (limited to 'arch/x86/kernel/fpu/init.c')
| -rw-r--r-- | arch/x86/kernel/fpu/init.c | 107 |
1 files changed, 2 insertions, 105 deletions
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c index 2f2b8c7ccb85..60dece392b3a 100644 --- a/arch/x86/kernel/fpu/init.c +++ b/arch/x86/kernel/fpu/init.c @@ -10,18 +10,6 @@ #include <linux/init.h> /* - * Initialize the TS bit in CR0 according to the style of context-switches - * we are using: - */ -static void fpu__init_cpu_ctx_switch(void) -{ - if (!boot_cpu_has(X86_FEATURE_EAGER_FPU)) - stts(); - else - clts(); -} - -/* * Initialize the registers found in all CPUs, CR0 and CR4: */ static void fpu__init_cpu_generic(void) @@ -58,7 +46,6 @@ void fpu__init_cpu(void) { fpu__init_cpu_generic(); fpu__init_cpu_xstate(); - fpu__init_cpu_ctx_switch(); } /* @@ -233,82 +220,16 @@ static void __init fpu__init_system_xstate_size_legacy(void) } /* - * FPU context switching strategies: - * - * Against popular belief, we don't do lazy FPU saves, due to the - * task migration complications it brings on SMP - we only do - * lazy FPU restores. - * - * 'lazy' is the traditional strategy, which is based on setting - * CR0::TS to 1 during context-switch (instead of doing a full - * restore of the FPU state), which causes the first FPU instruction - * after the context switch (whenever it is executed) to fault - at - * which point we lazily restore the FPU state into FPU registers. - * - * Tasks are of course under no obligation to execute FPU instructions, - * so it can easily happen that another context-switch occurs without - * a single FPU instruction being executed. If we eventually switch - * back to the original task (that still owns the FPU) then we have - * not only saved the restores along the way, but we also have the - * FPU ready to be used for the original task. - * - * 'lazy' is deprecated because it's almost never a performance win - * and it's much more complicated than 'eager'. - * - * 'eager' switching is by default on all CPUs, there we switch the FPU - * state during every context switch, regardless of whether the task - * has used FPU instructions in that time slice or not. This is done - * because modern FPU context saving instructions are able to optimize - * state saving and restoration in hardware: they can detect both - * unused and untouched FPU state and optimize accordingly. - * - * [ Note that even in 'lazy' mode we might optimize context switches - * to use 'eager' restores, if we detect that a task is using the FPU - * frequently. See the fpu->counter logic in fpu/internal.h for that. ] - */ -static enum { ENABLE, DISABLE } eagerfpu = ENABLE; - -/* * Find supported xfeatures based on cpu features and command-line input. * This must be called after fpu__init_parse_early_param() is called and * xfeatures_mask is enumerated. */ u64 __init fpu__get_supported_xfeatures_mask(void) { - /* Support all xfeatures known to us */ - if (eagerfpu != DISABLE) - return XCNTXT_MASK; - - /* Warning of xfeatures being disabled for no eagerfpu mode */ - if (xfeatures_mask & XFEATURE_MASK_EAGER) { - pr_err("x86/fpu: eagerfpu switching disabled, disabling the following xstate features: 0x%llx.\n", - xfeatures_mask & XFEATURE_MASK_EAGER); - } - - /* Return a mask that masks out all features requiring eagerfpu mode */ - return ~XFEATURE_MASK_EAGER; + return XCNTXT_MASK; } -/* - * Disable features dependent on eagerfpu. - */ -static void __init fpu__clear_eager_fpu_features(void) -{ - setup_clear_cpu_cap(X86_FEATURE_MPX); -} - -/* - * Pick the FPU context switching strategy: - * - * When eagerfpu is AUTO or ENABLE, we ensure it is ENABLE if either of - * the following is true: - * - * (1) the cpu has xsaveopt, as it has the optimization and doing eager - * FPU switching has a relatively low cost compared to a plain xsave; - * (2) the cpu has xsave features (e.g. MPX) that depend on eager FPU - * switching. Should the kernel boot with noxsaveopt, we support MPX - * with eager FPU switching at a higher cost. - */ +/* Legacy code to initialize eager fpu mode. */ static void __init fpu__init_system_ctx_switch(void) { static bool on_boot_cpu __initdata = 1; @@ -317,17 +238,6 @@ static void __init fpu__init_system_ctx_switch(void) on_boot_cpu = 0; WARN_ON_FPU(current->thread.fpu.fpstate_active); - - if (boot_cpu_has(X86_FEATURE_XSAVEOPT) && eagerfpu != DISABLE) - eagerfpu = ENABLE; - - if (xfeatures_mask & XFEATURE_MASK_EAGER) - eagerfpu = ENABLE; - - if (eagerfpu == ENABLE) - setup_force_cpu_cap(X86_FEATURE_EAGER_FPU); - - printk(KERN_INFO "x86/fpu: Using '%s' FPU context switches.\n", eagerfpu == ENABLE ? "eager" : "lazy"); } /* @@ -336,11 +246,6 @@ static void __init fpu__init_system_ctx_switch(void) */ static void __init fpu__init_parse_early_param(void) { - if (cmdline_find_option_bool(boot_command_line, "eagerfpu=off")) { - eagerfpu = DISABLE; - fpu__clear_eager_fpu_features(); - } - if (cmdline_find_option_bool(boot_command_line, "no387")) setup_clear_cpu_cap(X86_FEATURE_FPU); @@ -375,14 +280,6 @@ void __init fpu__init_system(struct cpuinfo_x86 *c) */ fpu__init_cpu(); - /* - * But don't leave CR0::TS set yet, as some of the FPU setup - * methods depend on being able to execute FPU instructions - * that will fault on a set TS, such as the FXSAVE in - * fpu__init_system_mxcsr(). - */ - clts(); - fpu__init_system_generic(); fpu__init_system_xstate_size_legacy(); fpu__init_system_xstate(); |