Messages in this thread | | | Date | Wed, 2 Aug 2017 15:33:33 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH] arm64: defconfig: enable fine-grained task level IRQ time accounting |
| |
On Wed, Aug 02, 2017 at 03:11:43PM +0200, Gregory CLEMENT wrote: > On lun., juil. 31 2017, Marcin Wojtas <mw@semihalf.com> wrote: > > 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. > > Who should take this patch? > > I think that all the defconfig under arm64 are merged through the > arm-soc subsystem, but this one is not really specific to a > SoC. However, as it was experimented on an mvebu SoC, if you agree I > can take it.
It's fine by me to go via arm-soc.
-- Catalin
| |