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Date: Thu, 18 Jun 2009 11:19:56 +0800 From: Lai Jiangshan <laijs@...fujitsu.com> To: Ingo Molnar <mingo@...e.hu> CC: Zhaolei <zhaolei@...fujitsu.com>, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>, Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org, fweisbec@...il.com, Li Zefan <lizf@...fujitsu.com>, Xiao Guangrong <xiaoguangrong@...fujitsu.com>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH RFC] softirq: fix ksoftirq starved Ingo Molnar wrote: > * Lai Jiangshan <laijs@...fujitsu.com> wrote: > >> --- a/kernel/sched.c >> +++ b/kernel/sched.c >> @@ -5307,6 +5307,7 @@ need_resched: >> release_kernel_lock(prev); >> need_resched_nonpreemptible: >> >> + schedule_softirq_check(); >> schedule_debug(prev); > > hm, this slows down the scheduler fast-path ... > > Ingo > > It's true. But: The overheads are: Overhead-A: the function call statement "schedule_softirq_check();" It can be gotten rid off by a macro or inline function. Overhead-B: __get_cpu_var() and the test statement. Overhead-C: do_softirq() In my patch, we test a variable and then call do_softirq() when the variable is true. do_softirq() can be called from process context or from schedule() or by any other ways, but it must be called and avoids starvation in this condition. So we need pay this overhead. It is no worse than before. Is it a critical thing when it slows down the scheduler fast-path because of the "Overhead-B"? Or I misunderstand something? Thanks, Lai. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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