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    Subject[PATCH] x86, apm: Make on_cpu0() use workqueue instead of work_on_cpu()
    Make APM schedule a work item on CPU0 instead of using the expensive
    work_on_cpu(); hopefully, this is the last user of work_on_cpu() and
    we can take out work_on_cpu() in not too distant future.

    Tested both paths. Seems to work fine.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    ---
    arch/x86/kernel/apm_32.c | 31 +++++++++++++++++++++++--------
    1 file changed, 23 insertions(+), 8 deletions(-)

    diff --git a/arch/x86/kernel/apm_32.c b/arch/x86/kernel/apm_32.c
    index d65464e..2bdb8c4 100644
    --- a/arch/x86/kernel/apm_32.c
    +++ b/arch/x86/kernel/apm_32.c
    @@ -605,28 +605,43 @@ static long __apm_bios_call(void *_call)
    return call->eax & 0xff;
    }

    +struct on_cpu0_arg {
    + struct work_struct work;
    + long (*fn)(void *);
    + struct apm_bios_call *call;
    + int ret;
    +};
    +
    +static void on_cpu0_workfn(struct work_struct *work)
    +{
    + struct on_cpu0_arg *arg = container_of(work, struct on_cpu0_arg, work);
    +
    + arg->ret = arg->fn(arg->call);
    +}
    +
    /* Run __apm_bios_call or __apm_bios_call_simple on CPU 0 */
    static int on_cpu0(long (*fn)(void *), struct apm_bios_call *call)
    {
    - int ret;
    + struct on_cpu0_arg arg = { .fn = fn, .call = call };

    - /* Don't bother with work_on_cpu in the common case, so we don't
    - * have to worry about OOM or overhead. */
    + /* directly invoke on_cpu0_workfn() in the common case */
    if (get_cpu() == 0) {
    - ret = fn(call);
    + on_cpu0_workfn(&arg.work);
    put_cpu();
    } else {
    put_cpu();
    - ret = work_on_cpu(0, fn, call);
    + INIT_WORK_ONSTACK(&arg.work, on_cpu0_workfn);
    + schedule_work_on(0, &arg.work);
    + flush_work(&arg.work);
    }

    /* work_on_cpu can fail with -ENOMEM */
    - if (ret < 0)
    - call->err = ret;
    + if (arg.ret < 0)
    + call->err = arg.ret;
    else
    call->err = (call->eax >> 8) & 0xff;

    - return ret;
    + return arg.ret;
    }

    /**

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