Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754431AbeALFgX (ORCPT + 1 other); Fri, 12 Jan 2018 00:36:23 -0500 Received: from mail.kernel.org ([198.145.29.99]:58422 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754259AbeALFgO (ORCPT ); Fri, 12 Jan 2018 00:36:14 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CDF752175C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=frederic@kernel.org From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Levin Alexander , Peter Zijlstra , Linus Torvalds , Hannes Frederic Sowa , "Paul E . McKenney" , Wanpeng Li , Dmitry Safonov , Thomas Gleixner , Eric Dumazet , Radu Rendec , Ingo Molnar , Stanislaw Gruszka , Paolo Abeni , Rik van Riel , Andrew Morton , David Miller Subject: [RFC PATCH 2/2] softirq: Per vector thread deferment Date: Fri, 12 Jan 2018 06:35:54 +0100 Message-Id: <1515735354-19279-3-git-send-email-frederic@kernel.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1515735354-19279-1-git-send-email-frederic@kernel.org> References: <1515735354-19279-1-git-send-email-frederic@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: Some softirq vectors can be more CPU hungry than others. Especially networking may sometimes deal with packet storm and need more CPU than IRQ tail can offer without inducing scheduler latencies. In this case the current code defers to ksoftirqd that behaves nicer. Now this nice behaviour can be bad for other IRQ vectors that usually need quick processing. To solve this we only defer to threading the vectors that outreached the time limit on IRQ tail processing and leave the others inline on real Soft-IRQs service. This is achieved using workqueues with per-CPU/per-vector worklets. Note ksoftirqd is not removed as it is still needed for threaded IRQs mode. Suggested-by: Linus Torvalds Signed-off-by: Frederic Weisbecker Cc: Dmitry Safonov Cc: Eric Dumazet Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Andrew Morton Cc: David Miller Cc: Hannes Frederic Sowa Cc: Ingo Molnar Cc: Levin Alexander Cc: Paolo Abeni Cc: Paul E. McKenney Cc: Radu Rendec Cc: Rik van Riel Cc: Stanislaw Gruszka Cc: Thomas Gleixner Cc: Wanpeng Li --- kernel/softirq.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 87 insertions(+), 3 deletions(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index fa267f7..0c817ec6 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -74,6 +74,13 @@ struct softirq_stat { static DEFINE_PER_CPU(struct softirq_stat, softirq_stat_cpu); +struct vector_work { + int vec; + struct work_struct work; +}; + +static DEFINE_PER_CPU(struct vector_work[NR_SOFTIRQS], vector_work_cpu); + /* * we cannot loop indefinitely here to avoid userspace starvation, * but we also don't want to introduce a worst case 1/HZ latency @@ -251,6 +258,70 @@ static inline bool lockdep_softirq_start(void) { return false; } static inline void lockdep_softirq_end(bool in_hardirq) { } #endif +static void vector_work_func(struct work_struct *work) +{ + struct vector_work *vector_work; + u32 pending; + int vec; + + vector_work = container_of(work, struct vector_work, work); + vec = vector_work->vec; + + local_irq_disable(); + pending = local_softirq_pending(); + account_irq_enter_time(current); + __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET); + lockdep_softirq_enter(); + set_softirq_pending(pending & ~(1 << vec)); + local_irq_enable(); + + if (pending & (1 << vec)) { + struct softirq_action *sa = &softirq_vec[vec]; + + kstat_incr_softirqs_this_cpu(vec); + trace_softirq_entry(vec); + sa->action(sa); + trace_softirq_exit(vec); + } + + local_irq_disable(); + + pending = local_softirq_pending(); + if (pending & (1 << vec)) + schedule_work_on(smp_processor_id(), work); + + lockdep_softirq_exit(); + account_irq_exit_time(current); + __local_bh_enable(SOFTIRQ_OFFSET); + local_irq_enable(); +} + +static int do_softirq_overrun(u32 overrun, u32 pending) +{ + struct softirq_action *h = softirq_vec; + int softirq_bit; + + if (!overrun) + return pending; + + overrun &= pending; + pending &= ~overrun; + + while ((softirq_bit = ffs(overrun))) { + struct vector_work *work; + unsigned int vec_nr; + + h += softirq_bit - 1; + vec_nr = h - softirq_vec; + work = this_cpu_ptr(&vector_work_cpu[vec_nr]); + schedule_work_on(smp_processor_id(), &work->work); + h++; + overrun >>= softirq_bit; + } + + return pending; +} + asmlinkage __visible void __softirq_entry __do_softirq(void) { struct softirq_stat *sstat = this_cpu_ptr(&softirq_stat_cpu); @@ -321,10 +392,13 @@ asmlinkage __visible void __softirq_entry __do_softirq(void) pending = local_softirq_pending(); if (pending) { - if (overrun || need_resched()) + if (need_resched()) { wakeup_softirqd(); - else - goto restart; + } else { + pending = do_softirq_overrun(overrun, pending); + if (pending) + goto restart; + } } lockdep_softirq_end(in_hardirq); @@ -661,10 +735,20 @@ void __init softirq_init(void) int cpu; for_each_possible_cpu(cpu) { + int i; + per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head; per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head; + + for (i = 0; i < NR_SOFTIRQS; i++) { + struct vector_work *work; + + work = &per_cpu(vector_work_cpu[i], cpu); + work->vec = i; + INIT_WORK(&work->work, vector_work_func); + } } open_softirq(TASKLET_SOFTIRQ, tasklet_action); -- 2.7.4