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    SubjectRe: [PATCH v2 2/4] x86, mwaitt: make delay method configurable
    On Tue, Jun 09, 2015 at 11:13:39AM +0800, Huang Rui wrote:
    > This patch introduces a kernel parameter (delay), user is able to configure
    > it at boot loader to choose different types of delay method.
    >
    > Default schema is to use TSC delay. This update can be more flexiable to
    > add new delay method.
    >
    > Suggested-by: Suravee Suthikulanit <suravee.suthikulpanit@amd.com>
    > Signed-off-by: Huang Rui <ray.huang@amd.com>
    > ---
    > arch/x86/include/asm/delay.h | 7 +++++++
    > arch/x86/kernel/setup.c | 19 +++++++++++++++++++
    > arch/x86/lib/delay.c | 12 +++++++++++-
    > 3 files changed, 37 insertions(+), 1 deletion(-)
    >
    > diff --git a/arch/x86/include/asm/delay.h b/arch/x86/include/asm/delay.h
    > index 9b3b4f2..99873ec 100644
    > --- a/arch/x86/include/asm/delay.h
    > +++ b/arch/x86/include/asm/delay.h
    > @@ -5,4 +5,11 @@
    >
    > void use_tsc_delay(void);
    >
    > +extern unsigned long boot_option_delay;
    > +
    > +enum delay_type {
    > + DELAY_LOOP=0,
    > + DELAY_TSC,
    > +};
    > +
    > #endif /* _ASM_X86_DELAY_H */
    > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
    > index 0b10698..cc2886d 100644
    > --- a/arch/x86/kernel/setup.c
    > +++ b/arch/x86/kernel/setup.c
    > @@ -111,6 +111,7 @@
    > #include <asm/mce.h>
    > #include <asm/alternative.h>
    > #include <asm/prom.h>
    > +#include <asm/delay.h>
    >
    > /*
    > * max_low_pfn_mapped: highest direct mapped pfn under 4GB
    > @@ -844,6 +845,24 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
    > return 0;
    > }
    >
    > +static int __init delay_setup(char *str)
    > +{
    > + if (!str)
    > + return -EINVAL;
    > +
    > + if (!strcmp(str, "tsc")) {
    > + pr_info("using tsc delay\n");
    > + boot_option_delay = DELAY_TSC;
    > + } else if (!strcmp(str, "loop")) {
    > + pr_info("using loop delay\n");
    > + boot_option_delay = DELAY_LOOP;
    > + } else
    > + return -1;

    What Peter said.

    And we did talk about this already in the last review. You guys want to
    drop all those kernel parameters and use MWAITX delay by default when:

    1. HW supports MWAITX

    *and*

    2. delay fits in u32.

    Kernel parameters is a bad bad idea.

    --
    Regards/Gruss,
    Boris.

    ECO tip #101: Trim your mails when you reply.
    --


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