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| author | Ingo Molnar <mingo@kernel.org> | 2015-05-01 07:59:04 (GMT) |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-05-19 13:48:09 (GMT) |
| commit | aeb997b9f2a2199c72b89b7a304cafc394e4202b (patch) | |
| tree | a9b963ffe79fee076fe09196714ba99f5326d254 /arch/x86/kernel/fpu | |
| parent | c47ada305de3803517ae64aa50686f644c5456fa (diff) | |
| download | linux-aeb997b9f2a2199c72b89b7a304cafc394e4202b.tar.xz | |
x86/fpu: Change fpu->fpregs_active from 'int' to 'char', add lazy switching comments
Improve the memory layout of 'struct fpu':
- change ->fpregs_active from 'int' to 'char' - it's just a single flag
and modern x86 CPUs can do efficient byte accesses.
- pack related fields closer to each other: often 'fpu->state' will not be
touched, while the other fields will - so pack them into a group.
Also add comments to each field, describing their purpose, and add
some background information about lazy restores.
Also fix an obsolete, lazy switching related comment in fpu_copy()'s description.
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/fpu')
| -rw-r--r-- | arch/x86/kernel/fpu/core.c | 6 | ||||
| -rw-r--r-- | arch/x86/kernel/fpu/xstate.c | 9 |
2 files changed, 7 insertions, 8 deletions
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index ac39616..97df457 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -227,10 +227,8 @@ EXPORT_SYMBOL_GPL(fpstate_init); /* * Copy the current task's FPU state to a new task's FPU context. * - * In the 'eager' case we just save to the destination context. - * - * In the 'lazy' case we save to the source context, mark the FPU lazy - * via stts() and copy the source context into the destination context. + * In both the 'eager' and the 'lazy' case we save hardware registers + * directly to the destination buffer. */ static void fpu_copy(struct fpu *dst_fpu, struct fpu *src_fpu) { diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 733a8ae..cd7f1a6 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -76,10 +76,11 @@ int cpu_has_xfeatures(u64 xfeatures_needed, const char **feature_name) EXPORT_SYMBOL_GPL(cpu_has_xfeatures); /* - * When executing XSAVEOPT (optimized XSAVE), if a processor implementation - * detects that an FPU state component is still (or is again) in its - * initialized state, it may clear the corresponding bit in the header.xfeatures - * field, and can skip the writeout of registers to the corresponding memory layout. + * When executing XSAVEOPT (or other optimized XSAVE instructions), if + * a processor implementation detects that an FPU state component is still + * (or is again) in its initialized state, it may clear the corresponding + * bit in the header.xfeatures field, and can skip the writeout of registers + * to the corresponding memory layout. * * This means that when the bit is zero, the state component might still contain * some previous - non-initialized register state. |