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David Alan Gilbert" , Markus Armbruster References: <20201119125940.20017-1-andrey.gruzdev@virtuozzo.com> <20201119125940.20017-4-andrey.gruzdev@virtuozzo.com> <20201119182516.GB6538@xz-x1> <1e35a550-a6a0-fbe2-ac8d-6844ce23b3fb@virtuozzo.com> <20201120150703.GE32525@xz-x1> <2797b4b6-b083-750f-385b-f0aa09730251@virtuozzo.com> <20201120164316.GC60522@xz-x1> From: Andrey Gruzdev Message-ID: Date: Fri, 20 Nov 2020 19:53:34 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: <20201120164316.GC60522@xz-x1> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [95.165.26.68] X-ClientProxiedBy: AM4PR0202CA0003.eurprd02.prod.outlook.com (2603:10a6:200:89::13) To VI1PR0802MB2510.eurprd08.prod.outlook.com (2603:10a6:800:ad::14) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.1.64] (95.165.26.68) by AM4PR0202CA0003.eurprd02.prod.outlook.com (2603:10a6:200:89::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3589.20 via Frontend Transport; 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envelope-from=andrey.gruzdev@virtuozzo.com; helo=EUR02-VE1-obe.outbound.protection.outlook.com X-Spam_score_int: -14 X-Spam_score: -1.5 X-Spam_bar: - X-Spam_report: (-1.5 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001, URG_BIZ=0.573 autolearn=no 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 20.11.2020 19:43, Peter Xu wrote: > On Fri, Nov 20, 2020 at 07:15:07PM +0300, Andrey Gruzdev wrote: >> Yeah, I think we can re-use the postcopy queue code for faulting pages. I'm >> worring a little about some additional overhead dealing with urgent request >> semaphore. Also, the code won't change a lot, something like: >> >> [...] >> /* In case of 'write-tracking' migration we first try >> * to poll UFFD and sse if we have write page fault event */ >> poll_fault_page(rs); >> >> again = true; >> found = get_queued_page(rs, &pss); >> >> if (!found) { >> /* priority queue empty, so just search for something dirty */ >> found = find_dirty_block(rs, &pss, &again); >> } >> [...] > > Could I ask what's the "urgent request semaphore"? Thanks, > These function use it (the correct name is 'rate_limit_sem'): void migration_make_urgent_request(void) { qemu_sem_post(&migrate_get_current()->rate_limit_sem); } void migration_consume_urgent_request(void) { qemu_sem_wait(&migrate_get_current()->rate_limit_sem); } They are called from ram_save_queue_pages and unqueue_page, accordingly, to control migration rate limiter. bool migration_rate_limit(void) { [...] /* * Wait for a delay to do rate limiting OR * something urgent to post the semaphore. */ int ms = s->iteration_start_time + BUFFER_DELAY - now; trace_migration_rate_limit_pre(ms); if (qemu_sem_timedwait(&s->rate_limit_sem, ms) == 0) { /* * We were woken by one or more urgent things but * the timedwait will have consumed one of them. * The service routine for the urgent wake will dec * the semaphore itself for each item it consumes, * so add this one we just eat back. */ qemu_sem_post(&s->rate_limit_sem); urgent = true; } [...] } -- Andrey Gruzdev, Principal Engineer Virtuozzo GmbH +7-903-247-6397 virtuzzo.com