Messages in this thread Patch in this message | | | Date | Mon, 1 Aug 2011 13:45:42 -0500 | From | Jack Steiner <> | Subject | Re: [PATCH v2] x86: Reduce clock calibration time during slave cpu startup |
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Reduce the startup time for slave cpus.
This patch adds hooks for an arch-specific function for clock calibration. These hooks are used on x86. If a newly started cpu has the same phys_proc_id as a core already active, use the already-calculated value of loops_per_jiffy.
The new code is used only on processor sockets that use the TSC for delay loops and have X86_FEATURE_CONSTANT_TSC.
This patch reduces the time required to start slave cpus on a 4096 cpu system from: 465 sec OLD 62 sec NEW
This reduces boot time on a 4096p system by almost 7 minutes. Nice...
Signed-off-by: Jack Steiner <steiner@sgi.com>
--- V2 - remove assumption that all cores in a socket have the same core frequency. the patch is enabled only if delay() uses the TSC & socket is CONSTANT_TSC.
Also see https://lkml.org/lkml/2010/12/14/511 for a previous discussion for similar improvement. This patch gives almost equivalent performance and is less intrusive.
arch/x86/kernel/smpboot.c | 16 +++++++++++----- arch/x86/kernel/tsc.c | 18 ++++++++++++++++++ init/calibrate.c | 16 ++++++++++++++++ 3 files changed, 45 insertions(+), 5 deletions(-)
Index: linux/arch/x86/kernel/smpboot.c =================================================================== --- linux.orig/arch/x86/kernel/smpboot.c 2011-07-26 08:01:11.611979781 -0500 +++ linux/arch/x86/kernel/smpboot.c 2011-08-01 13:25:42.544605719 -0500 @@ -207,23 +207,29 @@ static void __cpuinit smp_callin(void) * Need to setup vector mappings before we enable interrupts. */ setup_vector_irq(smp_processor_id()); + + /* + * Save our processor parameters. Note: this information + * is needed for clock calibration. + */ + smp_store_cpu_info(cpuid); + /* * Get our bogomips. + * Update loops_per_jiffy in cpu_data. Previous call to + * smp_store_cpu_info() stored a value that is close but not as + * accurate as the value just calculated. * * Need to enable IRQs because it can take longer and then * the NMI watchdog might kill us. */ local_irq_enable(); calibrate_delay(); + cpu_data(cpuid).loops_per_jiffy = loops_per_jiffy; local_irq_disable(); pr_debug("Stack at about %p\n", &cpuid); /* - * Save our processor parameters - */ - smp_store_cpu_info(cpuid); - - /* * This must be done before setting cpu_online_mask * or calling notify_cpu_starting. */ Index: linux/arch/x86/kernel/tsc.c =================================================================== --- linux.orig/arch/x86/kernel/tsc.c 2011-08-01 12:45:06.000000000 -0500 +++ linux/arch/x86/kernel/tsc.c 2011-08-01 13:26:20.244043188 -0500 @@ -995,3 +995,21 @@ void __init tsc_init(void) check_system_tsc_reliable(); } +/* + * Check if another cpu is in the same socket and has already been calibrated. + * If found, use the previous value. This assumes all cores in the same physical + * socket have the same core frequency. + */ +unsigned long __cpuinit calibrate_delay_is_known(void) +{ + int i, cpu = smp_processor_id(); + + if (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC)) + return 0; + + for_each_online_cpu(i) + if (cpu_data(i).phys_proc_id == cpu_data(cpu).phys_proc_id) + return cpu_data(i).loops_per_jiffy; + return 0; +} + Index: linux/init/calibrate.c =================================================================== --- linux.orig/init/calibrate.c 2011-07-26 08:01:15.571979739 -0500 +++ linux/init/calibrate.c 2011-07-27 08:39:35.691983745 -0500 @@ -243,6 +243,20 @@ recalibrate: return lpj; } +/* + * Check if cpu calibration delay is already known. For example, + * some processors with multi-core sockets may have all sockets + * use the same core frequency. It is not necessary to calibrate + * each core. + * + * Architectures should override this function if a faster calibration + * method is available. + */ +unsigned long __attribute__((weak)) __cpuinit calibrate_delay_is_known(void) +{ + return 0; +} + void __cpuinit calibrate_delay(void) { unsigned long lpj; @@ -257,6 +271,8 @@ void __cpuinit calibrate_delay(void) lpj = lpj_fine; pr_info("Calibrating delay loop (skipped), " "value calculated using timer frequency.. "); + } else if ((lpj = calibrate_delay_is_known())) { + ; } else if ((lpj = calibrate_delay_direct()) != 0) { if (!printed) pr_info("Calibrating delay using timer "
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