From 4445f2dd3386d44c03819fed3fd78a19e9ecdf10 Mon Sep 17 00:00:00 2001 From: Xie XiuQi Date: Wed, 17 Apr 2019 22:01:30 +0800 Subject: [PATCH] arm64: defconfig: enable fine-grained task level IRQ time accounting hulk inclusion category: feature bugzilla: 13257 CVE: NA Patch 168f2a8045 (arm64: defconfig: enable fine-grained task level IRQ time accounting) enable CONFIG_IRQ_TIME_ACCOUNTING by default. And we meet cpu usage problem in product team. So enable it on kernel by default. ---------------------------------------------- Tests showed, that under certain conditions, the summary number of jiffies spent on softirq/idle, which are counted by system statistics can be even below 10% of expected value, resulting in false load presentation. The issue was observed on the quad-core Marvell Armada 8k SoC, whose two 10G ports were bound into L2 bridge. Load was controlled by bidirectional UDP traffic, produced by a packet generator. Under such condition, the dominant load is softirq. With 100% single CPU occupation or without any activity (all CPUs 100% idle), total number of jiffies is 10000 (2500 per each core) in 10s interval. Also with other kind of load this was true. However below a saturation threshold it was observed, that with CPU which was occupied almost by softirqs only, the statistic were awkward. See the mpstat output: CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle all 0.00 0.00 0.13 0.00 0.00 0.55 0.00 0.00 0.00 99.32 0 0.00 0.00 0.00 0.00 0.00 23.08 0.00 0.00 0.00 76.92 1 0.00 0.00 0.40 0.00 0.00 0.00 0.00 0.00 0.00 99.60 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 Above would mean basically no total load, debug CPU0 occupied in 25%. Raw statistics, printed every 10s from /proc/stat unveiled a root cause - summary idle/softirq jiffies on loaded CPU were below 200, i.e. over 90% samples lost. All problems were gone after enabling fine granulity IRQ time accounting. This patch fixes possible wrong statistics processing by enabling CONFIG_IRQ_TIME_ACCOUNTING for arm64 platfroms, which is by default done on other architectures, e.g. x86 and arm. Tests showed no noticeable performance penalty, nor stability impact. Signed-off-by: Marcin Wojtas Signed-off-by: Gregory CLEMENT [XQ: enable this config on hulk_defconfig] Signed-off-by: Xie XiuQi Reviewed-by: Cheng Jian Signed-off-by: Yang Yingliang --- arch/arm64/configs/hulk_defconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/configs/hulk_defconfig b/arch/arm64/configs/hulk_defconfig index 74774acf2ca5..f070422854bd 100644 --- a/arch/arm64/configs/hulk_defconfig +++ b/arch/arm64/configs/hulk_defconfig @@ -79,7 +79,7 @@ CONFIG_PREEMPT_VOLUNTARY=y # CONFIG_VIRT_CPU_ACCOUNTING=y CONFIG_VIRT_CPU_ACCOUNTING_GEN=y -# CONFIG_IRQ_TIME_ACCOUNTING is not set +CONFIG_IRQ_TIME_ACCOUNTING=y CONFIG_HAVE_SCHED_AVG_IRQ=y CONFIG_BSD_PROCESS_ACCT=y CONFIG_BSD_PROCESS_ACCT_V3=y -- GitLab