summaryrefslogtreecommitdiff
path: root/arch/arm64/configs
diff options
context:
space:
mode:
authorMarcin Wojtas <mw@semihalf.com>2017-07-31 23:22:11 +0300
committerGregory CLEMENT <gregory.clement@free-electrons.com>2017-08-03 15:25:52 +0300
commita168f2a80458095ccdc03ea777d5d469be3934ed (patch)
treeacea9cd544748d8b82dbcacb703a6a629e844110 /arch/arm64/configs
parent3fe42235570ff673e551bb31a236359c77098c7b (diff)
downloadlinux-a168f2a80458095ccdc03ea777d5d469be3934ed.tar.xz
arm64: defconfig: enable fine-grained task level IRQ time accounting
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 <mw@semihalf.com> Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Diffstat (limited to 'arch/arm64/configs')
-rw-r--r--arch/arm64/configs/defconfig1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig
index 2ca3a25cc3b3..e9286af948be 100644
--- a/arch/arm64/configs/defconfig
+++ b/arch/arm64/configs/defconfig
@@ -3,6 +3,7 @@ CONFIG_POSIX_MQUEUE=y
CONFIG_AUDIT=y
CONFIG_NO_HZ_IDLE=y
CONFIG_HIGH_RES_TIMERS=y
+CONFIG_IRQ_TIME_ACCOUNTING=y
CONFIG_BSD_PROCESS_ACCT=y
CONFIG_BSD_PROCESS_ACCT_V3=y
CONFIG_TASKSTATS=y