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I would like to know how to use the functions, kernel_fpu_begin and kernel_fpu_end, correctly. I did try to google this, but the other forums were not clear enough for me ...
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  1. #1
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    How to use kernel_fpu_begin and kernel_fpu_end correctly?


    I would like to know how to use the functions, kernel_fpu_begin and kernel_fpu_end, correctly.

    I did try to google this, but the other forums were not clear enough for me to understand.

    I did try this doing these functions, but I got couple of errors. I think it may have to do with the include header file.
    May be it is the wrong one.

    The code below is something I tried.
    Any help is really appreciated thanks.

    Code:
    #include <asm/i387.h>
    
    static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
    {
    	kernel_fpu_begin();
    
    	struct tcp_sock *tp = tcp_sk(sk);
    	struct vegas *vegas = inet_csk_ca(sk);
    	int target_queue_size;
    	double avgRTT_Mult, rtt_Mult; 
    	
    	target_queue_size = 100;
    	avgRTT_Mult = 0.99609375; //(255/256)
    	rtt_Mult    = 0.00390625; //(1/256)
    
    
    	avgRTT = (avgRTT_Mult*avgRtt) + (rtt_Mult*rtt);
    
    	kernel_fpu_end();	
    }

  2. #2
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    1
    It's not available at kernel runtime either with my Debian setup. Any help would be great - thanks!!!
    Being a newbie, the URL is not allowed - here's more info:
    ------------------
    From: Linus Torvalds <torvalds@linux-foundation.org>

    commit b6c66418dcad0fcf83cd1d0a39482db37bf4fc41 upstream.

    Touching TS_USEDFPU without touching CR0.TS is confusing, so don't do
    it. By moving it into the callers, we always do the TS_USEDFPU next to
    the CR0.TS accesses in the source code, and it's much easier to see how
    the two go hand in hand.

    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/include/asm/i387.h | 9 ++++++---
    1 file changed, 6 insertions(+), 3 deletions(-)
    --- a/arch/x86/include/asm/i387.h
    +++ b/arch/x86/include/asm/i387.h
    @@ -259,7 +259,6 @@ static inline void fpu_save_init(struct
    static inline void __save_init_fpu(struct task_struct *tsk)
    {
    fpu_save_init(&tsk->thread.fpu);
    - task_thread_info(tsk)->status &= ~TS_USEDFPU;
    }

    static inline int fpu_fxrstor_checking(struct fpu *fpu)
    @@ -290,6 +289,7 @@ static inline void __unlazy_fpu(struct t
    {
    if (task_thread_info(tsk)->status & TS_USEDFPU) {
    __save_init_fpu(tsk);
    + task_thread_info(tsk)->status &= ~TS_USEDFPU;
    stts();
    } else
    tsk->fpu_counter = 0;
    @@ -356,9 +356,11 @@ static inline void kernel_fpu_begin(void

    WARN_ON_ONCE(!irq_fpu_usable());
    preempt_disable();
    - if (me->status & TS_USEDFPU)
    + if (me->status & TS_USEDFPU) {
    __save_init_fpu(me->task);
    - else
    + me->status &= ~TS_USEDFPU;
    + /* We do 'stts()' in kernel_fpu_end() */
    + } else
    clts();
    }

    @@ -449,6 +451,7 @@ static inline void save_init_fpu(struct
    WARN_ON_ONCE(!(task_thread_info(tsk)->status & TS_USEDFPU));
    preempt_disable();
    __save_init_fpu(tsk);
    + task_thread_info(tsk)->status &= ~TS_USEDFPU;
    stts();
    preempt_enable();
    }
    Last edited by xcub; 06-26-2012 at 06:09 AM. Reason: Clarification

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