Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxx> --- Following the discussion around commit 9791554b [MIPS,prctl: add PR_[GS]ET_FP_MODE prctl options for MIPS] or <http://patchwork.linux-mips.org/patch/8899/> and Leonid's observation <http://www.linux-mips.org/cgi-bin/mesg.cgi?a=linux-mips&i=54B02115.7090609%40imgtec.com> in particular, I agree this would best be done with an IPI, however such an improvement is independent of the changes made as a part of this series so I took the minimal approach and left the solution implemented so far unchanged. Especially as Leonid says he's got a patch already available. linux-mips-process-fp-context.diff Index: linux-sfr-test/arch/mips/kernel/process.c =================================================================== --- linux-sfr-test.orig/arch/mips/kernel/process.c 2015-11-13 00:36:09.885716000 +0000 +++ linux-sfr-test/arch/mips/kernel/process.c 2015-11-16 13:50:18.962058000 +0000 @@ -570,6 +570,60 @@ void arch_trigger_all_cpu_backtrace(bool smp_call_function(arch_dump_stack, NULL, 1); } +/* + * Make the FP context available for mode changes. + */ +static void mips_get_fp_context(struct task_struct *task) +{ + unsigned long switch_count; + struct task_struct *t; + + /* Save FP & vector context, then disable FPU & MSA. */ + if (task->signal == current->signal) + lose_fpu(1); + + /* Prevent any threads from obtaining live FP context. */ + atomic_set(&task->mm->context.fp_mode_switching, 1); + smp_mb__after_atomic(); + + /* + * If there are multiple online CPUs then wait until all threads + * whose FP mode is about to change have been context switched. + * This approach allows us to only worry about whether an FP mode + * switch is in progress when FP is first used in a tasks time + * slice. Pretty much all of the mode switch overhead can thus + * be confined to cases where mode switches are actually occurring. + * That is, to here. However for the thread performing the mode + * switch it may take a while... + */ + if (num_online_cpus() > 1) { + spin_lock_irq(&task->sighand->siglock); + + for_each_thread(task, t) { + if (t == current) + continue; + + switch_count = t->nvcsw + t->nivcsw; + + do { + spin_unlock_irq(&task->sighand->siglock); + cond_resched(); + spin_lock_irq(&task->sighand->siglock); + } while ((t->nvcsw + t->nivcsw) == switch_count); + } + + spin_unlock_irq(&task->sighand->siglock); + } +} + +/* + * Allow threads to use FP again. + */ +static void mips_put_fp_context(struct task_struct *task) +{ + atomic_set(&task->mm->context.fp_mode_switching, 0); +} + int mips_get_process_fp_mode(struct task_struct *task) { int value = 0; @@ -585,7 +639,6 @@ int mips_get_process_fp_mode(struct task int mips_set_process_fp_mode(struct task_struct *task, unsigned int value) { const unsigned int known_bits = PR_FP_MODE_FR | PR_FP_MODE_FRE; - unsigned long switch_count; struct task_struct *t; /* Check the value is valid */ @@ -603,41 +656,7 @@ int mips_set_process_fp_mode(struct task if (!(value & PR_FP_MODE_FR) && cpu_has_fpu && cpu_has_mips_r6) return -EOPNOTSUPP; - /* Save FP & vector context, then disable FPU & MSA */ - if (task->signal == current->signal) - lose_fpu(1); - - /* Prevent any threads from obtaining live FP context */ - atomic_set(&task->mm->context.fp_mode_switching, 1); - smp_mb__after_atomic(); - - /* - * If there are multiple online CPUs then wait until all threads whose - * FP mode is about to change have been context switched. This approach - * allows us to only worry about whether an FP mode switch is in - * progress when FP is first used in a tasks time slice. Pretty much all - * of the mode switch overhead can thus be confined to cases where mode - * switches are actually occuring. That is, to here. However for the - * thread performing the mode switch it may take a while... - */ - if (num_online_cpus() > 1) { - spin_lock_irq(&task->sighand->siglock); - - for_each_thread(task, t) { - if (t == current) - continue; - - switch_count = t->nvcsw + t->nivcsw; - - do { - spin_unlock_irq(&task->sighand->siglock); - cond_resched(); - spin_lock_irq(&task->sighand->siglock); - } while ((t->nvcsw + t->nivcsw) == switch_count); - } - - spin_unlock_irq(&task->sighand->siglock); - } + mips_get_fp_context(task); /* * There are now no threads of the process with live FP context, so it @@ -659,8 +678,7 @@ int mips_set_process_fp_mode(struct task clear_tsk_thread_flag(t, TIF_HYBRID_FPREGS); } - /* Allow threads to use FP again */ - atomic_set(&task->mm->context.fp_mode_switching, 0); + mips_put_fp_context(task); return 0; }
