On Tue 2014-06-17 16:52:00, Petr Mládek wrote:
> What about replacing the above changes in kernel/printk/printk.c with
> the following ones:
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index ea2d5f6962ed..e00a9600f5fa 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -266,6 +266,7 @@ static u32 clear_idx;
> #define LOG_ALIGN __alignof__(struct printk_log)
> #endif
> #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
> +#define __LOG_CPU_MIN_BUF_LEN (1 << CONFIG_LOG_CPU_MIN_BUF_SHIFT)
> static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
> static char *log_buf = __log_buf;
> static u32 log_buf_len = __LOG_BUF_LEN;
> @@ -842,12 +843,52 @@ static int __init log_buf_len_setup(char *str)
> }
> early_param("log_buf_len", log_buf_len_setup);
>
> +static unsigned __init default_len_by_cpu_num(void)
> +{
> + int cpu_extra;
> + unsigned extra_cpu_log_size;
> +
> + /*
> + * archs should set up cpu_possible_bits properly with
> + * set_cpu_possible() after setup_arch() but just in
> + * case lets ensure this is valid.
> + */
> + if (num_possible_cpus() <= 1)
> + return 0;
> +
> + cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MIN_BUF_LEN;
> + /* make sure that the buffer is aligned */
> + cpu_extra %= LOG_ALIGN;
> + extra_cpu_log_size = roundup_pow_of_two(cpu_extra + __LOG_BUF_LEN);
> +
> + if (cpu_extra <= __LOG_BUF_LEN / 2)
> + return 0;
> +
> + pr_info("log_buf_len cpu_extra contribution: %d\n", cpu_extra);
> + pr_info("log_buf_len min size: %d\n", __LOG_BUF_LEN);
> +
> + return extra_cpu_log_size;
> +}
> +
> void __init setup_log_buf(int early)
> {
> unsigned long flags;
> char *new_log_buf;
> int free;
>
> + /* nope when already allocated earlier */
> + if (log_buf != __log_buf)
> + return;
> +
> + /*
> + * The default size need to be increased on systems with many CPUs.
> + * It is done only when an exact size is not forced by log_buf_len=n
> + * kernel parameter.
> + */
> + if (!new_log_buf_len)
> + new_log_buf_len = default_len_by_cpu_num();
Also I forgot to explain that default_len_by_cpu_num()
could be called even in the early stage. In this case
it returns zero because num_possible_cpus() returns 1. It means that
the buffer wont be allocated at this stage. I think that it is pretty
safe.
If you want to avoid this speculative call, you might use:
if (!new_log_buf_len && !early)
new_log_buf_len = default_len_by_cpu_num();
> + /* nope when nobody wants to increase the size after all */
> if (!new_log_buf_len)
> return;
>
> --
> 1.8.4
Best Regards,
Petr
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
