To show time info in kernel log earlier and help optimizing kernel boot time, printk adds a debug hook "boot_printk_clock_fn()" for capable platform which has accurate clock in early boot phase.
This patch will add early param setup option, so that user can chose to provide a tsc based early printk clock simply by adding in command line: "boot_tsc=xxxxM" (xxxxM is the stable TSC freq). Signed-off-by: Feng Tang <[email protected]> --- arch/x86/kernel/tsc.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 74392d9..d99eb70 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -281,6 +281,57 @@ static int __init tsc_setup(char *str) __setup("tsc=", tsc_setup); + +/* + * This is to provide a not-so-accurate clock for printk timestamp in + * early boot phase (before sched_clock is setup).It could be used for + * analyzing/optimising kernel boot time and tools like bootchart. + * + * User can use it by simply append something like + * "boot_tsc=1881M" + * to cmdline for a platform with a stable 1881MHz TSC. + */ +static u64 boot_tsc_mhz; +static u64 boot_tsc_offset; + +static u64 boot_tsc_clock(void) +{ + u64 cur_tsc, cur_ns; + + cur_tsc = rdtsc(); + cur_tsc -= boot_tsc_offset; + + /* return value in ns */ + cur_ns = div64_u64(cur_tsc * 1000, boot_tsc_mhz); + return cur_ns; +} + +static int __init boot_tsc_setup(char *p) +{ + u64 tsc_hz; + + if (!p) + return -EINVAL; + + boot_tsc_offset = rdtsc(); + + tsc_hz = memparse(p, &p); + boot_tsc_mhz = div64_u64(tsc_hz, 1024 * 1024); + if (boot_tsc_mhz == 0) + return -EINVAL; + + pr_info("TSC has run for %lld us\n", + div64_u64(boot_tsc_offset, boot_tsc_mhz)); + + /* Setup the early printk clock */ + boot_printk_clock_fn = boot_tsc_clock; + pr_info("TSC: Setup early printk timestamp with %lldM TSC.", + boot_tsc_mhz); + + return 0; +} +early_param("boot_tsc", boot_tsc_setup); + #define MAX_RETRIES 5 #define SMI_TRESHOLD 50000 -- 2.7.4
