From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 426BDC54EBE for ; Sat, 14 Jan 2023 02:20:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231463AbjANCUF (ORCPT ); Fri, 13 Jan 2023 21:20:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46292 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231455AbjANCT7 (ORCPT ); Fri, 13 Jan 2023 21:19:59 -0500 Received: from out30-111.freemail.mail.aliyun.com (out30-111.freemail.mail.aliyun.com [115.124.30.111]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 63AAA8CBC8; Fri, 13 Jan 2023 18:19:56 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046049;MF=hsiangkao@linux.alibaba.com;NM=1;PH=DS;RN=11;SR=0;TI=SMTPD_---0VZW9rHd_1673662790; Received: from 30.27.94.170(mailfrom:hsiangkao@linux.alibaba.com fp:SMTPD_---0VZW9rHd_1673662790) by smtp.aliyun-inc.com; Sat, 14 Jan 2023 10:19:52 +0800 Message-ID: Date: Sat, 14 Jan 2023 10:19:50 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH] workqueue: Add WQ_SCHED_FIFO To: Nathan Huckleberry , Lai Jiangshan , Tejun Heo Cc: Sandeep Dhavale , Daeho Jeong , Eric Biggers , Sami Tolvanen , Jonathan Corbet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-erofs@lists.ozlabs.org References: <20230113210703.62107-1-nhuck@google.com> From: Gao Xiang In-Reply-To: <20230113210703.62107-1-nhuck@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Nathan! On 2023/1/14 05:07, Nathan Huckleberry wrote: > Add a WQ flag that allows workqueues to use SCHED_FIFO with the least > imporant RT priority. This can reduce scheduler latency for IO > post-processing when the CPU is under load without impacting other RT > workloads. This has been shown to improve app startup time on Android > [1]. Thank you all for your effort on this. Unfortunately I have no time to setup the test [1] until now. If it can be addressed as a new workqueue feature, that would be much helpful to me. Otherwise, I still need to find a way to resolve the latest Android + EROFS latency problem. > > Scheduler latency affects several drivers as evidenced by [1], [2], [3], > [4]. Some of these drivers have moved post-processing into IRQ context. > However, this can cause latency spikes for real-time threads and jitter > related jank on Android. Using a workqueue with SCHED_FIFO improves > scheduler latency without causing latency problems for RT threads. softirq context is actually mainly for post-interrupt handling I think. but considering decompression/verification/decryption all workload are much complex than that and less important than real post-interrupt handling. I don't think softirq context is the best place to handle these CPU-intensive jobs. Beside, it could cause some important work moving to softirqd unexpectedly in the extreme cases. Also such many post-processing jobs are as complex as they could sleep so that softirq context is unsuitable as well. Anyway, I second this proposal if possible: Acked-by: Gao Xiang Thanks, Gao Xiang > > [1]: > https://lore.kernel.org/linux-erofs/20230106073502.4017276-1-dhavale@google.com/ > [2]: > https://lore.kernel.org/linux-f2fs-devel/20220802192437.1895492-1-daeho43@gmail.com/ > [3]: > https://lore.kernel.org/dm-devel/20220722093823.4158756-4-nhuck@google.com/ > [4]: > https://lore.kernel.org/dm-crypt/20200706173731.3734-1-ignat@cloudflare.com/ > > This change has been tested on dm-verity with the following fio config: > > [global] > time_based > runtime=120 > > [do-verify] > ioengine=sync > filename=/dev/testing > rw=randread > direct=1 > > [burn_8x90%_qsort] > ioengine=cpuio > cpuload=90 > numjobs=8 > cpumode=qsort > > Before: > clat (usec): min=13, max=23882, avg=29.56, stdev=113.29 READ: > bw=122MiB/s (128MB/s), 122MiB/s-122MiB/s (128MB/s-128MB/s), io=14.3GiB > (15.3GB), run=120001-120001msec > > After: > clat (usec): min=13, max=23137, avg=19.96, stdev=105.71 READ: > bw=180MiB/s (189MB/s), 180MiB/s-180MiB/s (189MB/s-189MB/s), io=21.1GiB > (22.7GB), run=120012-120012msec > > Cc: Sandeep Dhavale > Cc: Daeho Jeong > Cc: Eric Biggers > Cc: Sami Tolvanen > Signed-off-by: Nathan Huckleberry > --- > Documentation/core-api/workqueue.rst | 12 ++++++++++ > include/linux/workqueue.h | 9 +++++++ > kernel/workqueue.c | 36 +++++++++++++++++++++------- > 3 files changed, 48 insertions(+), 9 deletions(-) > > diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst > index 3b22ed137662..26faf2806c66 100644 > --- a/Documentation/core-api/workqueue.rst > +++ b/Documentation/core-api/workqueue.rst > @@ -216,6 +216,18 @@ resources, scheduled and executed. > > This flag is meaningless for unbound wq. > > +``WQ_SCHED_FIFO`` > + Work items of a fifo wq are queued to the fifo > + worker-pool of the target cpu. Fifo worker-pools are > + served by worker threads with scheduler policy SCHED_FIFO and > + the least important real-time priority. This can be useful > + for workloads where low latency is imporant. > + > + A workqueue cannot be both high-priority and fifo. > + > + Note that normal and fifo worker-pools don't interact with > + each other. Each maintains its separate pool of workers and > + implements concurrency management among its workers. > > ``max_active`` > -------------- > diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h > index ac551b8ee7d9..43a4eeaf8ff4 100644 > --- a/include/linux/workqueue.h > +++ b/include/linux/workqueue.h > @@ -134,6 +134,10 @@ struct workqueue_attrs { > * @nice: nice level > */ > int nice; > + /** > + * @sched_fifo: is using SCHED_FIFO > + */ > + bool sched_fifo; > > /** > * @cpumask: allowed CPUs > @@ -334,6 +338,11 @@ enum { > * http://thread.gmane.org/gmane.linux.kernel/1480396 > */ > WQ_POWER_EFFICIENT = 1 << 7, > + /* > + * Low real-time priority workqueues can reduce scheduler latency > + * for latency sensitive workloads like IO post-processing. > + */ > + WQ_SCHED_FIFO = 1 << 8, > > __WQ_DESTROYING = 1 << 15, /* internal: workqueue is destroying */ > __WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */ > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 5dc67aa9d696..99c5e0a3dc28 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -85,7 +85,7 @@ enum { > WORKER_NOT_RUNNING = WORKER_PREP | WORKER_CPU_INTENSIVE | > WORKER_UNBOUND | WORKER_REBOUND, > > - NR_STD_WORKER_POOLS = 2, /* # standard pools per cpu */ > + NR_STD_WORKER_POOLS = 3, /* # standard pools per cpu */ > > UNBOUND_POOL_HASH_ORDER = 6, /* hashed by pool->attrs */ > BUSY_WORKER_HASH_ORDER = 6, /* 64 pointers */ > @@ -1949,7 +1949,8 @@ static struct worker *create_worker(struct worker_pool *pool) > > if (pool->cpu >= 0) > snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id, > - pool->attrs->nice < 0 ? "H" : ""); > + pool->attrs->sched_fifo ? "F" : > + (pool->attrs->nice < 0 ? "H" : "")); > else > snprintf(id_buf, sizeof(id_buf), "u%d:%d", pool->id, id); > > @@ -1958,7 +1959,11 @@ static struct worker *create_worker(struct worker_pool *pool) > if (IS_ERR(worker->task)) > goto fail; > > - set_user_nice(worker->task, pool->attrs->nice); > + if (pool->attrs->sched_fifo) > + sched_set_fifo_low(worker->task); > + else > + set_user_nice(worker->task, pool->attrs->nice); > + > kthread_bind_mask(worker->task, pool->attrs->cpumask); > > /* successful, attach the worker to the pool */ > @@ -4323,9 +4328,17 @@ static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu, > > static int alloc_and_link_pwqs(struct workqueue_struct *wq) > { > - bool highpri = wq->flags & WQ_HIGHPRI; > + int pool_index = 0; > int cpu, ret; > > + if (wq->flags & WQ_HIGHPRI && wq->flags & WQ_SCHED_FIFO) > + return -EINVAL; > + > + if (wq->flags & WQ_HIGHPRI) > + pool_index = 1; > + if (wq->flags & WQ_SCHED_FIFO) > + pool_index = 2; > + > if (!(wq->flags & WQ_UNBOUND)) { > wq->cpu_pwqs = alloc_percpu(struct pool_workqueue); > if (!wq->cpu_pwqs) > @@ -4337,7 +4350,7 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq) > struct worker_pool *cpu_pools = > per_cpu(cpu_worker_pools, cpu); > > - init_pwq(pwq, wq, &cpu_pools[highpri]); > + init_pwq(pwq, wq, &cpu_pools[pool_index]); > > mutex_lock(&wq->mutex); > link_pwq(pwq); > @@ -4348,13 +4361,13 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq) > > cpus_read_lock(); > if (wq->flags & __WQ_ORDERED) { > - ret = apply_workqueue_attrs(wq, ordered_wq_attrs[highpri]); > + ret = apply_workqueue_attrs(wq, ordered_wq_attrs[pool_index]); > /* there should only be single pwq for ordering guarantee */ > WARN(!ret && (wq->pwqs.next != &wq->dfl_pwq->pwqs_node || > wq->pwqs.prev != &wq->dfl_pwq->pwqs_node), > "ordering guarantee broken for workqueue %s\n", wq->name); > } else { > - ret = apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]); > + ret = apply_workqueue_attrs(wq, unbound_std_wq_attrs[pool_index]); > } > cpus_read_unlock(); > > @@ -6138,7 +6151,8 @@ static void __init wq_numa_init(void) > */ > void __init workqueue_init_early(void) > { > - int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL }; > + int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL, 0 }; > + bool std_sched_fifo[NR_STD_WORKER_POOLS] = { false, false, true }; > int i, cpu; > > BUILD_BUG_ON(__alignof__(struct pool_workqueue) < __alignof__(long long)); > @@ -6158,8 +6172,10 @@ void __init workqueue_init_early(void) > BUG_ON(init_worker_pool(pool)); > pool->cpu = cpu; > cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu)); > - pool->attrs->nice = std_nice[i++]; > + pool->attrs->nice = std_nice[i]; > + pool->attrs->sched_fifo = std_sched_fifo[i]; > pool->node = cpu_to_node(cpu); > + i++; > > /* alloc pool ID */ > mutex_lock(&wq_pool_mutex); > @@ -6174,6 +6190,7 @@ void __init workqueue_init_early(void) > > BUG_ON(!(attrs = alloc_workqueue_attrs())); > attrs->nice = std_nice[i]; > + attrs->sched_fifo = std_sched_fifo[i]; > unbound_std_wq_attrs[i] = attrs; > > /* > @@ -6183,6 +6200,7 @@ void __init workqueue_init_early(void) > */ > BUG_ON(!(attrs = alloc_workqueue_attrs())); > attrs->nice = std_nice[i]; > + attrs->sched_fifo = std_sched_fifo[i]; > attrs->no_numa = true; > ordered_wq_attrs[i] = attrs; > }