linux-kernel - Re: [PATCH v5 1/2] timers: Don't wake ktimersoftd on every tick

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Date:   Fri, 13 Jul 2018 14:01:45 +0200 (CEST)
From:   Anna-Maria Gleixner <anna-maria@...utronix.de>
To:     Haris Okanovic <haris.okanovic@...com>
cc:     linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        harisokn@...il.com, bigeasy@...utronix.de, tglx@...utronix.de,
        julia.cartwright@...com, gratian.crisan@...com, daniel@...stot.me,
        efault@....de
Subject: Re: [PATCH v5 1/2] timers: Don't wake ktimersoftd on every tick

Hi Haris,

On Thu, 28 Jun 2018, Haris Okanovic wrote:

> Collect expired timers in interrupt context to avoid overhead of waking
> ktimersoftd on every scheduler tick.
> 
> This is implemented by storing lists of expired timers in the timer_base
> struct, which is updated by the interrupt routing on each tick in
> run_local_timers(). TIMER softirq (ktimersoftd) is then raised only when
> one or more expired timers are collected.
> 
> Performance impact on a 2core Intel Atom E3825 system:
>  * reduction in small latency spikes measured by cyclictest
>  * ~30% fewer context-switches measured by perf
>  * run_local_timers() execution time increases by 0.2 measured by TSC
> 

I'm also working on timer improvements at the moment. When I fixed all
my bugs in my implementation (there is a last horrible one), I'm very
interested in integrating your patches into my testing to be able to
give you a tested-by.

Thanks,

	Anna-Maria