From fa8a7094ba1679b4b9b443e0ac9f5e046c79ee8d Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 22 Jun 2009 11:56:24 +0900 Subject: x86: implement percpu_alloc kernel parameter According to Andi, it isn't clear whether lpage allocator is worth the trouble as there are many processors where PMD TLB is far scarcer than PTE TLB. The advantage or disadvantage probably depends on the actual size of percpu area and specific processor. As performance degradation due to TLB pressure tends to be highly workload specific and subtle, it is difficult to decide which way to go without more data. This patch implements percpu_alloc kernel parameter to allow selecting which first chunk allocator to use to ease debugging and testing. While at it, make sure all the failure paths report why something failed to help determining why certain allocator isn't working. Also, kill the "Great future plan" comment which had already been realized quite some time ago. [ Impact: allow explicit percpu first chunk allocator selection ] Signed-off-by: Tejun Heo Reported-by: Jan Beulich Cc: Andi Kleen Cc: Ingo Molnar --- Documentation/kernel-parameters.txt | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'Documentation') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 08def8deb5f..ecad946920d 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -1882,6 +1882,12 @@ and is between 256 and 4096 characters. It is defined in the file Format: { 0 | 1 } See arch/parisc/kernel/pdc_chassis.c + percpu_alloc= [X86] Select which percpu first chunk allocator to use. + Allowed values are one of "lpage", "embed" and "4k". + See comments in arch/x86/kernel/setup_percpu.c for + details on each allocator. This parameter is primarily + for debugging and performance comparison. + pf. [PARIDE] See Documentation/blockdev/paride.txt. -- cgit v1.2.3