On 02/20, Andy Lutomirski wrote:
>
> We have eager and lazy fpu modes, introduced in:
>
> 304bceda6a18 x86, fpu: use non-lazy fpu restore for processors supporting
> xsave
>
> The result is rather messy. There are two code paths in almost all of the
> FPU code, and only one of them (the eager case) is tested frequently, since
> most kernel developers have new enough hardware that we use eagerfpu.
>
> It seems that, on any remotely recent hardware, eagerfpu is a win:
> glibc uses SSE2, so laziness is probably overoptimistic, and, in any
> case, manipulating TS is far slower that saving and restoring the full
> state.
>
> To try to shake out any latent issues on old hardware, this changes
> the default to eager on all CPUs. If no performance or functionality
> problems show up, a subsequent patch could remove lazy mode entirely.
>
> Signed-off-by: Andy Lutomirski <l...@amacapital.net>
> ---
> arch/x86/kernel/xsave.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
> index 0de1fae2bdf0..1928c8f34ce5 100644
> --- a/arch/x86/kernel/xsave.c
> +++ b/arch/x86/kernel/xsave.c
> @@ -637,8 +637,8 @@ static void __init xstate_enable_boot_cpu(void)
> prepare_fx_sw_frame();
> setup_init_fpu_buf();
>
> - /* Auto enable eagerfpu for xsaveopt */
> - if (cpu_has_xsaveopt && eagerfpu != DISABLE)
> + /* Auto enable eagerfpu for everyone */
> + if (eagerfpu != DISABLE)
> eagerfpu = ENABLE;
Well, but if we want this change then perhaps we should simply change
the default value? This way "AUTO" still can work.
Oleg.
--- x/arch/x86/kernel/xsave.c
+++ x/arch/x86/kernel/xsave.c
@@ -563,7 +563,7 @@ static void __init setup_init_fpu_buf(vo
xsave_state_booting(init_xstate_buf, -1);
}
-static enum { AUTO, ENABLE, DISABLE } eagerfpu = AUTO;
+static enum { AUTO, ENABLE, DISABLE } eagerfpu = ENABLE;
static int __init eager_fpu_setup(char *s)
{
if (!strcmp(s, "on"))
--
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