From: john stultz Currently on NUMAQ hardware we set tsc_disable=1 because on multi-node NUMAQ hardware the TSC is not synced. However, it is safe to use the TSC on single node NUMAQs. Thus this patch only disables the TSC if num_online_nodes() > 1. This should fix performance issues seen w/ -mm by mbligh on elm3b132 (which is a single node NUMAQ). These performance issues originated because with mainline code, the function that disables the TSC runs after time_init, thus the TSC is used regardless, allowing for possible timekeeping errors on multi-node systems. With my new timekeeping work we do not select the TSC until later, so we see the TSC has been disabled and use the slower PIT instead as the original code intends. This caused the performance regression. While this patch allows the TSC to be used safely only on single node NUMAQs, multi-node NUMAQs may still see a performance drop from using the PIT, but this is necessary as using unsynched TSCs will result in incorrect timekeeping. For test results, please see the graph: http://test.kernel.org/perf/kernbench.elm3b132.png 2.6.16-rc1-mm5: without this patch 2.6.16-rc1-mm5+p22126: with this patch This patch also fixes the typo'ed function name. Signed-off-by: John Stultz Acked-by: Martin J. Bligh Signed-off-by: Andrew Morton --- arch/i386/kernel/numaq.c | 10 ++++++---- 1 files changed, 6 insertions(+), 4 deletions(-) diff -puN arch/i386/kernel/numaq.c~i386-dont-disable-the-tsc-on-single-node-numaqs arch/i386/kernel/numaq.c --- devel/arch/i386/kernel/numaq.c~i386-dont-disable-the-tsc-on-single-node-numaqs 2006-02-13 04:31:54.000000000 -0800 +++ devel-akpm/arch/i386/kernel/numaq.c 2006-02-13 04:31:54.000000000 -0800 @@ -79,10 +79,12 @@ int __init get_memcfg_numaq(void) return 1; } -static int __init numaq_dsc_disable(void) +static int __init numaq_tsc_disable(void) { - printk(KERN_DEBUG "NUMAQ: disabling TSC\n"); - tsc_disable = 1; + if (num_online_nodes() > 1) { + printk(KERN_DEBUG "NUMAQ: disabling TSC\n"); + tsc_disable = 1; + } return 0; } -core_initcall(numaq_dsc_disable); +arch_initcall(numaq_tsc_disable); _