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authorAl Viro <viro@zeniv.linux.org.uk>2022-09-02 03:50:12 +0200
committerMatt Turner <mattst88@gmail.com>2023-02-25 05:14:22 +0100
commit050966666047b5013fe44944cef9e9605bdf6cfe (patch)
tree6c25361790776289d998deb98c50694bf41ff37f /arch/alpha/kernel/asm-offsets.c
parentalpha/boot/misc: trim unused declarations (diff)
downloadlinux-050966666047b5013fe44944cef9e9605bdf6cfe.tar.xz
linux-050966666047b5013fe44944cef9e9605bdf6cfe.zip
alpha: lazy FPU switching
On each context switch we save the FPU registers on stack of old process and restore FPU registers from the stack of new one. That allows us to avoid doing that each time we enter/leave the kernel mode; however, that can get suboptimal in some cases. For one thing, we don't need to bother saving anything for kernel threads. For another, if between entering and leaving the kernel a thread gives CPU up more than once, it will do useless work, saving the same values every time, only to discard the saved copy as soon as it returns from switch_to(). Alternative solution: * move the array we save into from switch_stack to thread_info * have a (thread-synchronous) flag set when we save them * have another flag set when they should be restored on return to userland. * do *NOT* save/restore them in do_switch_stack()/undo_switch_stack(). * restore on the exit to user mode if the restore flag had been set. Clear both flags. * on context switch, entry to fork/clone/vfork, before entry into do_signal() and on entry into straced syscall save the registers and set the 'saved' flag unless it had been already set. * on context switch set the 'restore' flag as well. * have copy_thread() set both flags for child, so the registers would be restored once the child returns to userland. * use the saved data in setup_sigcontext(); have restore_sigcontext() set both flags and copy from sigframe to save area. * teach ptrace to look for FPU registers in thread_info instead of switch_stack. * teach isolated accesses to FPU registers (rdfpcr, wrfpcr, etc.) to check the 'saved' flag (under preempt_disable()) and work with the save area if it's been set; if 'saved' flag is found upon write access, set 'restore' flag as well. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Matt Turner <mattst88@gmail.com>
Diffstat (limited to 'arch/alpha/kernel/asm-offsets.c')
-rw-r--r--arch/alpha/kernel/asm-offsets.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/alpha/kernel/asm-offsets.c b/arch/alpha/kernel/asm-offsets.c
index 2e125e5c1508..b121294bee26 100644
--- a/arch/alpha/kernel/asm-offsets.c
+++ b/arch/alpha/kernel/asm-offsets.c
@@ -17,6 +17,8 @@ void foo(void)
DEFINE(TI_TASK, offsetof(struct thread_info, task));
DEFINE(TI_FLAGS, offsetof(struct thread_info, flags));
DEFINE(TI_CPU, offsetof(struct thread_info, cpu));
+ DEFINE(TI_FP, offsetof(struct thread_info, fp));
+ DEFINE(TI_STATUS, offsetof(struct thread_info, status));
BLANK();
DEFINE(TASK_BLOCKED, offsetof(struct task_struct, blocked));