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    Subject[PATCH] printk: Shrink printk_sched buffer size, eliminate it when !CONFIG_PRINTK
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    The size of the per-cpu printk_sched buf is much larger
    than necessary. The maximum sched message emitted is
    ~80 bytes. Shrink the allocation for this printk_sched
    buffer from 512 bytes to 128.

    printk_sched creates an unnecessary per-cpu buffer when
    CONFIG_PRINTK is not enabled. Remove it when appropriate
    so embedded uses save a bit of space too.

    Signed-off-by: Joe Perches <joe@perches.com>
    ---
    kernel/printk.c | 14 ++++++++++----
    1 files changed, 10 insertions(+), 4 deletions(-)

    diff --git a/kernel/printk.c b/kernel/printk.c
    index 32462d2..61cff0b 100644
    --- a/kernel/printk.c
    +++ b/kernel/printk.c
    @@ -1726,24 +1726,30 @@ int is_console_locked(void)
    }

    /*
    - * Delayed printk version, for scheduler-internal messages:
    + * Delayed printk version, for scheduler-internal messages.
    + * Not the normal 512 as it's a bit wasteful, sched messages are short,
    + * and 128 is more than sufficient for all current messages.
    */
    -#define PRINTK_BUF_SIZE 512
    +#define PRINTK_SCHED_BUF_SIZE 128

    #define PRINTK_PENDING_WAKEUP 0x01
    #define PRINTK_PENDING_SCHED 0x02

    static DEFINE_PER_CPU(int, printk_pending);
    -static DEFINE_PER_CPU(char [PRINTK_BUF_SIZE], printk_sched_buf);
    +#ifdef CONFIG_PRINTK
    +static DEFINE_PER_CPU(char [PRINTK_SCHED_BUF_SIZE], printk_sched_buf);
    +#endif

    void printk_tick(void)
    {
    if (__this_cpu_read(printk_pending)) {
    int pending = __this_cpu_xchg(printk_pending, 0);
    +#ifdef CONFIG_PRINTK
    if (pending & PRINTK_PENDING_SCHED) {
    char *buf = __get_cpu_var(printk_sched_buf);
    printk(KERN_WARNING "[sched_delayed] %s", buf);
    }
    +#endif
    if (pending & PRINTK_PENDING_WAKEUP)
    wake_up_interruptible(&log_wait);
    }
    @@ -2189,7 +2195,7 @@ int printk_sched(const char *fmt, ...)
    buf = __get_cpu_var(printk_sched_buf);

    va_start(args, fmt);
    - r = vsnprintf(buf, PRINTK_BUF_SIZE, fmt, args);
    + r = vsnprintf(buf, PRINTK_SCHED_BUF_SIZE, fmt, args);
    va_end(args);

    __this_cpu_or(printk_pending, PRINTK_PENDING_SCHED);



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