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Thu, 9 Sep 2021 02:30:08 +0000 (GMT) Received: from [9.211.114.163] (unknown [9.211.114.163]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP; Thu, 9 Sep 2021 02:30:08 +0000 (GMT) Subject: Re: [PATCH] coroutine: resize pool periodically instead of limiting size To: Stefan Hajnoczi , qemu-devel@nongnu.org References: <20210901160923.525651-1-stefanha@redhat.com> From: Daniele Buono Message-ID: <677df3db-fb9d-f64d-62f5-98857db5e6e6@linux.vnet.ibm.com> Date: Wed, 8 Sep 2021 22:30:09 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: zYJPbqWpVVEWQoILRq_rhsO0M1GtfkZN X-Proofpoint-ORIG-GUID: wbEp1turQKBzBQyA3UoWGEYuXbD1Kq8f X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391, 18.0.790 definitions=2021-09-08_10:2021-09-07, 2021-09-08 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 adultscore=0 impostorscore=0 mlxlogscore=999 spamscore=0 mlxscore=0 lowpriorityscore=0 malwarescore=0 clxscore=1011 suspectscore=0 priorityscore=1501 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2109030001 definitions=main-2109090012 Received-SPF: none client-ip=148.163.158.5; envelope-from=dbuono@linux.vnet.ibm.com; helo=mx0b-001b2d01.pphosted.com X-Spam_score_int: -38 X-Spam_score: -3.9 X-Spam_bar: --- X-Spam_report: (-3.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-1.922, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , atheurer@redhat.com, jhopper@redhat.com, Tingting Mao , Honghao Wang , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Serge Guelton Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Stefan, the patch looks great. Thank you for debugging the performance issue that was happening with SafeStack. On 9/2/2021 4:10 AM, Stefan Hajnoczi wrote: > On Wed, Sep 01, 2021 at 05:09:23PM +0100, Stefan Hajnoczi wrote: >> It was reported that enabling SafeStack reduces IOPS significantly >> (>25%) with the following fio benchmark on virtio-blk using a NVMe host >> block device: >> >> # fio --rw=randrw --bs=4k --iodepth=64 --runtime=1m --direct=1 \ >> --filename=/dev/vdb --name=job1 --ioengine=libaio --thread \ >> --group_reporting --numjobs=16 --time_based \ >> --output=/tmp/fio_result >> >> Serge Guelton and I found that SafeStack is not really at fault, it just >> increases the cost of coroutine creation. This fio workload exhausts the >> coroutine pool and coroutine creation becomes a bottleneck. Previous >> work by Honghao Wang also pointed to excessive coroutine creation. >> >> Creating new coroutines is expensive due to allocating new stacks with >> mmap(2) and mprotect(2). Currently there are thread-local and global >> pools that recycle old Coroutine objects and their stacks but the >> hardcoded size limit of 64 for thread-local pools and 128 for the global >> pool is insufficient for the fio benchmark shown above. >> >> This patch changes the coroutine pool algorithm to a simple thread-local >> pool without a size limit. Threads periodically shrink the pool down to >> a size sufficient for the maximum observed number of coroutines. >> >> This is a very simple algorithm. Fancier things could be done like >> keeping a minimum number of coroutines around to avoid latency when a >> new coroutine is created after a long period of inactivity. Another >> thought is to stop the timer when the pool size is zero for power saving >> on threads that aren't using coroutines. However, I'd rather not add >> bells and whistles unless they are really necessary. I agree we should aim at something that is as simple as possible. However keeping a minumum number of coroutines could be useful to avoid performance regressions from the previous version. I wouldn't say restore the global pool - that's way too much trouble - but keeping the old "pool size" configuration parameter as the miniumum pool size could be a good idea to maintain the previous performance in cases where the dynamic pool shrinks too much. >> >> The global pool is removed by this patch. It can help to hide the fact >> that local pools are easily exhausted, but it's doesn't fix the root >> cause. I don't think there is a need for a global pool because QEMU's >> threads are long-lived, so let's keep things simple. >> >> Performance of the above fio benchmark is as follows: >> >> Before After >> IOPS 60k 97k >> >> Memory usage varies over time as needed by the workload: >> >> VSZ (KB) RSS (KB) >> Before fio 4705248 843128 >> During fio 5747668 (+ ~100 MB) 849280 >> After fio 4694996 (- ~100 MB) 845184 >> >> This confirms that coroutines are indeed being freed when no longer >> needed. >> >> Thanks to Serge Guelton for working on identifying the bottleneck with >> me! >> >> Reported-by: Tingting Mao >> Cc: Serge Guelton >> Cc: Honghao Wang >> Cc: Paolo Bonzini >> Cc: Daniele Buono >> Signed-off-by: Stefan Hajnoczi >> --- >> include/qemu/coroutine-pool-timer.h | 36 +++++++++++++++++ >> include/qemu/coroutine.h | 7 ++++ >> iothread.c | 6 +++ >> util/coroutine-pool-timer.c | 35 ++++++++++++++++ >> util/main-loop.c | 5 +++ >> util/qemu-coroutine.c | 62 ++++++++++++++--------------- >> util/meson.build | 1 + >> 7 files changed, 119 insertions(+), 33 deletions(-) >> create mode 100644 include/qemu/coroutine-pool-timer.h >> create mode 100644 util/coroutine-pool-timer.c > > Adding Andrew and Jenifer in case they have thoughts on improving QEMU's > coroutine pool algorithm. > >> >> diff --git a/include/qemu/coroutine-pool-timer.h b/include/qemu/coroutine-pool-timer.h >> new file mode 100644 >> index 0000000000..c0b520ce99 >> --- /dev/null >> +++ b/include/qemu/coroutine-pool-timer.h >> @@ -0,0 +1,36 @@ >> +/* >> + * QEMU coroutine pool timer >> + * >> + * Copyright (c) 2021 Red Hat, Inc. >> + * >> + * SPDX-License-Identifier: LGPL-2.1-or-later >> + * >> + * This work is licensed under the terms of the GNU LGPL, version 2.1 or later. >> + * See the COPYING.LIB file in the top-level directory. >> + * >> + */ >> +#ifndef COROUTINE_POOL_TIMER_H >> +#define COROUTINE_POOL_TIMER_H >> + >> +#include "qemu/osdep.h" >> +#include "block/aio.h" >> + >> +/** >> + * A timer that periodically resizes this thread's coroutine pool, freeing >> + * memory if there are too many unused coroutines. >> + * >> + * Threads that make heavy use of coroutines should use this. Failure to resize >> + * the coroutine pool can lead to large amounts of memory sitting idle and >> + * never being used after the first time. >> + */ >> +typedef struct { >> + QEMUTimer *timer; >> +} CoroutinePoolTimer; >> + >> +/* Call this before the thread runs the AioContext */ >> +void coroutine_pool_timer_init(CoroutinePoolTimer *pt, AioContext *ctx); >> + >> +/* Call this before the AioContext from the init function is destroyed */ >> +void coroutine_pool_timer_cleanup(CoroutinePoolTimer *pt); >> + >> +#endif /* COROUTINE_POOL_TIMER_H */ >> diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h >> index 4829ff373d..fdb2955ff9 100644 >> --- a/include/qemu/coroutine.h >> +++ b/include/qemu/coroutine.h >> @@ -122,6 +122,13 @@ bool qemu_in_coroutine(void); >> */ >> bool qemu_coroutine_entered(Coroutine *co); >> >> +/** >> + * Optionally call this function periodically to shrink the thread-local pool >> + * down. Spiky workloads can create many coroutines and then never reach that >> + * level again. Shrinking the pool reclaims memory in this case. >> + */ >> +void qemu_coroutine_pool_periodic_resize(void); >> + >> /** >> * Provides a mutex that can be used to synchronise coroutines >> */ >> diff --git a/iothread.c b/iothread.c >> index ddbbde61f7..39a24f1a55 100644 >> --- a/iothread.c >> +++ b/iothread.c >> @@ -23,6 +23,7 @@ >> #include "qemu/error-report.h" >> #include "qemu/rcu.h" >> #include "qemu/main-loop.h" >> +#include "qemu/coroutine-pool-timer.h" >> >> typedef ObjectClass IOThreadClass; >> >> @@ -42,6 +43,7 @@ DECLARE_CLASS_CHECKERS(IOThreadClass, IOTHREAD, >> static void *iothread_run(void *opaque) >> { >> IOThread *iothread = opaque; >> + CoroutinePoolTimer co_pool_timer; >> >> rcu_register_thread(); >> /* >> @@ -53,6 +55,8 @@ static void *iothread_run(void *opaque) >> iothread->thread_id = qemu_get_thread_id(); >> qemu_sem_post(&iothread->init_done_sem); >> >> + coroutine_pool_timer_init(&co_pool_timer, iothread->ctx); >> + >> while (iothread->running) { >> /* >> * Note: from functional-wise the g_main_loop_run() below can >> @@ -74,6 +78,8 @@ static void *iothread_run(void *opaque) >> } >> } >> >> + coroutine_pool_timer_cleanup(&co_pool_timer); >> + >> g_main_context_pop_thread_default(iothread->worker_context); >> rcu_unregister_thread(); >> return NULL; >> diff --git a/util/coroutine-pool-timer.c b/util/coroutine-pool-timer.c >> new file mode 100644 >> index 0000000000..36d3216718 >> --- /dev/null >> +++ b/util/coroutine-pool-timer.c >> @@ -0,0 +1,35 @@ >> +/* >> + * QEMU coroutine pool timer >> + * >> + * Copyright (c) 2021 Red Hat, Inc. >> + * >> + * SPDX-License-Identifier: LGPL-2.1-or-later >> + * >> + * This work is licensed under the terms of the GNU LGPL, version 2.1 or later. >> + * See the COPYING.LIB file in the top-level directory. >> + * >> + */ >> +#include "qemu/coroutine-pool-timer.h" >> + >> +static void coroutine_pool_timer_cb(void *opaque) >> +{ >> + CoroutinePoolTimer *pt = opaque; >> + int64_t expiry_time_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + >> + 15 * NANOSECONDS_PER_SECOND; >> + >> + qemu_coroutine_pool_periodic_resize(); >> + timer_mod(pt->timer, expiry_time_ns); >> +} >> + >> +void coroutine_pool_timer_init(CoroutinePoolTimer *pt, AioContext *ctx) >> +{ >> + pt->timer = aio_timer_new(ctx, QEMU_CLOCK_REALTIME, SCALE_NS, >> + coroutine_pool_timer_cb, pt); >> + coroutine_pool_timer_cb(pt); >> +} >> + >> +void coroutine_pool_timer_cleanup(CoroutinePoolTimer *pt) >> +{ >> + timer_free(pt->timer); >> + pt->timer = NULL; >> +} >> diff --git a/util/main-loop.c b/util/main-loop.c >> index 06b18b195c..23342e2215 100644 >> --- a/util/main-loop.c >> +++ b/util/main-loop.c >> @@ -33,6 +33,7 @@ >> #include "qemu/error-report.h" >> #include "qemu/queue.h" >> #include "qemu/compiler.h" >> +#include "qemu/coroutine-pool-timer.h" >> >> #ifndef _WIN32 >> #include >> @@ -131,6 +132,7 @@ static int qemu_signal_init(Error **errp) >> >> static AioContext *qemu_aio_context; >> static QEMUBH *qemu_notify_bh; >> +static CoroutinePoolTimer main_loop_co_pool_timer; >> >> static void notify_event_cb(void *opaque) >> { >> @@ -181,6 +183,9 @@ int qemu_init_main_loop(Error **errp) >> g_source_set_name(src, "io-handler"); >> g_source_attach(src, NULL); >> g_source_unref(src); >> + >> + coroutine_pool_timer_init(&main_loop_co_pool_timer, qemu_aio_context); >> + >> return 0; >> } >> >> diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c >> index 38fb6d3084..105dbfa89e 100644 >> --- a/util/qemu-coroutine.c >> +++ b/util/qemu-coroutine.c >> @@ -20,15 +20,11 @@ >> #include "qemu/coroutine_int.h" >> #include "block/aio.h" >> >> -enum { >> - POOL_BATCH_SIZE = 64, >> -}; >> - >> /** Free list to speed up creation */ >> -static QSLIST_HEAD(, Coroutine) release_pool = QSLIST_HEAD_INITIALIZER(pool); >> -static unsigned int release_pool_size; >> static __thread QSLIST_HEAD(, Coroutine) alloc_pool = QSLIST_HEAD_INITIALIZER(pool); >> static __thread unsigned int alloc_pool_size; >> +static __thread unsigned int num_coroutines; >> +static __thread unsigned int max_coroutines_this_slice; >> static __thread Notifier coroutine_pool_cleanup_notifier; >> >> static void coroutine_pool_cleanup(Notifier *n, void *value) >> @@ -48,26 +44,19 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque) >> >> if (CONFIG_COROUTINE_POOL) { >> co = QSLIST_FIRST(&alloc_pool); >> - if (!co) { >> - if (release_pool_size > POOL_BATCH_SIZE) { >> - /* Slow path; a good place to register the destructor, too. */ >> - if (!coroutine_pool_cleanup_notifier.notify) { >> - coroutine_pool_cleanup_notifier.notify = coroutine_pool_cleanup; >> - qemu_thread_atexit_add(&coroutine_pool_cleanup_notifier); >> - } >> - >> - /* This is not exact; there could be a little skew between >> - * release_pool_size and the actual size of release_pool. But >> - * it is just a heuristic, it does not need to be perfect. >> - */ >> - alloc_pool_size = qatomic_xchg(&release_pool_size, 0); >> - QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool); >> - co = QSLIST_FIRST(&alloc_pool); >> - } >> - } >> if (co) { >> QSLIST_REMOVE_HEAD(&alloc_pool, pool_next); >> alloc_pool_size--; >> + } else { >> + if (!coroutine_pool_cleanup_notifier.notify) { >> + coroutine_pool_cleanup_notifier.notify = coroutine_pool_cleanup; >> + qemu_thread_atexit_add(&coroutine_pool_cleanup_notifier); >> + } >> + } >> + >> + num_coroutines++; >> + if (num_coroutines > max_coroutines_this_slice) { >> + max_coroutines_this_slice = num_coroutines; >> } >> } >> >> @@ -86,21 +75,28 @@ static void coroutine_delete(Coroutine *co) >> co->caller = NULL; >> >> if (CONFIG_COROUTINE_POOL) { >> - if (release_pool_size < POOL_BATCH_SIZE * 2) { >> - QSLIST_INSERT_HEAD_ATOMIC(&release_pool, co, pool_next); >> - qatomic_inc(&release_pool_size); >> - return; >> - } >> - if (alloc_pool_size < POOL_BATCH_SIZE) { >> - QSLIST_INSERT_HEAD(&alloc_pool, co, pool_next); >> - alloc_pool_size++; >> - return; >> - } >> + num_coroutines--; >> + QSLIST_INSERT_HEAD(&alloc_pool, co, pool_next); >> + alloc_pool_size++; >> + return; >> } >> >> qemu_coroutine_delete(co); >> } >> >> +void qemu_coroutine_pool_periodic_resize(void) >> +{ >> + unsigned pool_size_target = max_coroutines_this_slice - num_coroutines; >> + max_coroutines_this_slice = num_coroutines; >> + >> + while (alloc_pool_size > pool_size_target) { >> + Coroutine *co = QSLIST_FIRST(&alloc_pool); >> + QSLIST_REMOVE_HEAD(&alloc_pool, pool_next); >> + qemu_coroutine_delete(co); >> + alloc_pool_size--; >> + } >> +} >> + >> void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co) >> { >> QSIMPLEQ_HEAD(, Coroutine) pending = QSIMPLEQ_HEAD_INITIALIZER(pending); >> diff --git a/util/meson.build b/util/meson.build >> index 779f413c86..06241097d2 100644 >> --- a/util/meson.build >> +++ b/util/meson.build >> @@ -63,6 +63,7 @@ if have_block >> util_ss.add(files('buffer.c')) >> util_ss.add(files('bufferiszero.c')) >> util_ss.add(files('coroutine-@0@.c'.format(config_host['CONFIG_COROUTINE_BACKEND']))) >> + util_ss.add(files('coroutine-pool-timer.c')) >> util_ss.add(files('hbitmap.c')) >> util_ss.add(files('hexdump.c')) >> util_ss.add(files('iova-tree.c')) >> -- >> 2.31.1 >>