| From 75af76d0a34e048651a6af311781d7206b6964c7 Mon Sep 17 00:00:00 2001 |
| From: Mel Gorman <mgorman@techsingularity.net> |
| Date: Fri, 16 Oct 2020 17:28:32 +0200 |
| Subject: intel_idle: Ignore _CST if control cannot be taken from the platform |
| |
| From: Mel Gorman <mgorman@techsingularity.net> |
| |
| commit 75af76d0a34e048651a6af311781d7206b6964c7 upstream. |
| |
| e6d4f08a6776 ("intel_idle: Use ACPI _CST on server systems") avoids |
| enabling c-states that have been disabled by the platform with the |
| exception of C1E. |
| |
| Unfortunately, BIOS implementations are not always consistent in terms |
| of how capabilities are advertised and control cannot always be handed |
| over. If control cannot be handed over then intel_idle reports that "ACPI |
| _CST not found or not usable" but does not clear acpi_state_table.count |
| meaning the information is still partially used. |
| |
| This patch ignores ACPI information if CST control cannot be requested from |
| the platform. This was only observed on a number of Haswell platforms that |
| had identical CPUs but not identical BIOS versions. While this problem |
| may be rare overall, 24 separate test cases bisected to this specific |
| commit across 4 separate test machines and is worth addressing. If the |
| situation occurs, the kernel behaves as it did before commit e6d4f08a6776 |
| and uses any c-states that are discovered. |
| |
| The affected test cases were all ones that involved a small number of |
| processes -- exec microbenchmark, pipe microbenchmark, git test suite, |
| netperf, tbench with one client and system call microbenchmark. Each |
| case benefits from being able to use turboboost which is prevented if the |
| lower c-states are unavailable. This may mask real regressions specific |
| to older hardware so it is worth addressing. |
| |
| C-state status before and after the patch |
| |
| 5.9.0-vanilla POLL latency:0 disabled:0 default:enabled |
| 5.9.0-vanilla C1 latency:2 disabled:0 default:enabled |
| 5.9.0-vanilla C1E latency:10 disabled:0 default:enabled |
| 5.9.0-vanilla C3 latency:33 disabled:1 default:disabled |
| 5.9.0-vanilla C6 latency:133 disabled:1 default:disabled |
| 5.9.0-ignore-cst-v1r1 POLL latency:0 disabled:0 default:enabled |
| 5.9.0-ignore-cst-v1r1 C1 latency:2 disabled:0 default:enabled |
| 5.9.0-ignore-cst-v1r1 C1E latency:10 disabled:0 default:enabled |
| 5.9.0-ignore-cst-v1r1 C3 latency:33 disabled:0 default:enabled |
| 5.9.0-ignore-cst-v1r1 C6 latency:133 disabled:0 default:enabled |
| |
| Patch enables C3/C6. |
| |
| Netperf UDP_STREAM |
| |
| netperf-udp |
| 5.5.0 5.9.0 |
| vanilla ignore-cst-v1r1 |
| Hmean send-64 193.41 ( 0.00%) 226.54 * 17.13%* |
| Hmean send-128 392.16 ( 0.00%) 450.54 * 14.89%* |
| Hmean send-256 769.94 ( 0.00%) 881.85 * 14.53%* |
| Hmean send-1024 2994.21 ( 0.00%) 3468.95 * 15.85%* |
| Hmean send-2048 5725.60 ( 0.00%) 6628.99 * 15.78%* |
| Hmean send-3312 8468.36 ( 0.00%) 10288.02 * 21.49%* |
| Hmean send-4096 10135.46 ( 0.00%) 12387.57 * 22.22%* |
| Hmean send-8192 17142.07 ( 0.00%) 19748.11 * 15.20%* |
| Hmean send-16384 28539.71 ( 0.00%) 30084.45 * 5.41%* |
| |
| Fixes: e6d4f08a6776 ("intel_idle: Use ACPI _CST on server systems") |
| Signed-off-by: Mel Gorman <mgorman@techsingularity.net> |
| Cc: 5.6+ <stable@vger.kernel.org> # 5.6+ |
| Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| drivers/idle/intel_idle.c | 7 +++---- |
| 1 file changed, 3 insertions(+), 4 deletions(-) |
| |
| --- a/drivers/idle/intel_idle.c |
| +++ b/drivers/idle/intel_idle.c |
| @@ -1212,14 +1212,13 @@ static bool __init intel_idle_acpi_cst_e |
| if (!intel_idle_cst_usable()) |
| continue; |
| |
| - if (!acpi_processor_claim_cst_control()) { |
| - acpi_state_table.count = 0; |
| - return false; |
| - } |
| + if (!acpi_processor_claim_cst_control()) |
| + break; |
| |
| return true; |
| } |
| |
| + acpi_state_table.count = 0; |
| pr_debug("ACPI _CST not found or not usable\n"); |
| return false; |
| } |
