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 X-Spam-Level: X-Spam-Status: No, score=-18.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3F4A1C6379F for ; Mon, 19 Jul 2021 21:20:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0D61A61175 for ; Mon, 19 Jul 2021 21:20:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1387822AbhGSUf3 (ORCPT ); Mon, 19 Jul 2021 16:35:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:55272 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354316AbhGSUXp (ORCPT ); Mon, 19 Jul 2021 16:23:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626728656; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=mDzv4r/nKmHoEY/y/S31BYFYyCyd3ydFbHliB67gI10=; b=ZypLFW8xkdb+aFF0+TYJSwLYYxoRilXOWlapqh1Q0ab+HWjaMvE0qNEOCF513jq3mnmqTP Xf4u2FDuMC+aK3ODd32jdxf25UYJNFcPF83xDHDsZLdNQc/A71nuN6orvpzXWMyG0jYPOB Bq1S03cjjNY2iDIPeK2DVGMW8wGjzSU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-590-Lt425qk5P-W4_BxnE0IKdQ-1; Mon, 19 Jul 2021 17:04:15 -0400 X-MC-Unique: Lt425qk5P-W4_BxnE0IKdQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A49EA100C610; Mon, 19 Jul 2021 21:04:13 +0000 (UTC) Received: from fuller.cnet (ovpn-112-6.gru2.redhat.com [10.97.112.6]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 79F4A2706E; Mon, 19 Jul 2021 21:04:01 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id E87DB4172ED4; Mon, 19 Jul 2021 18:03:55 -0300 (-03) Date: Mon, 19 Jul 2021 18:03:55 -0300 From: Marcelo Tosatti To: Stefan Hajnoczi Cc: linux-kernel@vger.kernel.org, Daniel Lezcano , Stefano Garzarella , Ming Lei , "Michael S . Tsirkin" , Jens Axboe , Jason Wang , linux-block@vger.kernel.org, "Rafael J. Wysocki" , virtualization@lists.linux-foundation.org, linux-pm@vger.kernel.org, Christoph Hellwig Subject: Re: [RFC 1/3] cpuidle: add poll_source API Message-ID: <20210719210355.GA46373@fuller.cnet> References: <20210713161906.457857-1-stefanha@redhat.com> <20210713161906.457857-2-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210713161906.457857-2-stefanha@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Stefan, On Tue, Jul 13, 2021 at 05:19:04PM +0100, Stefan Hajnoczi wrote: > Introduce an API for adding cpuidle poll callbacks: > > struct poll_source_ops { > void (*start)(struct poll_source *src); > void (*stop)(struct poll_source *src); > void (*poll)(struct poll_source *src); > }; > > int poll_source_register(struct poll_source *src); > int poll_source_unregister(struct poll_source *src); > > When cpuidle enters the poll state it invokes ->start() and then invokes > ->poll() repeatedly from the busy wait loop. Finally ->stop() is invoked > when the busy wait loop finishes. > > The ->poll() function should check for activity and cause > TIF_NEED_RESCHED to be set in order to stop the busy wait loop. > > This API is intended to be used by drivers that can cheaply poll for > events. Participating in cpuidle polling allows them to avoid interrupt > latencies during periods where the CPU is going to poll anyway. > > Note that each poll_source is bound to a particular CPU. The API is > mainly intended to by used by drivers that have multiple queues with irq > affinity. > > Signed-off-by: Stefan Hajnoczi > --- > drivers/cpuidle/Makefile | 1 + > include/linux/poll_source.h | 53 +++++++++++++++++++ > drivers/cpuidle/poll_source.c | 99 +++++++++++++++++++++++++++++++++++ > drivers/cpuidle/poll_state.c | 6 +++ > 4 files changed, 159 insertions(+) > create mode 100644 include/linux/poll_source.h > create mode 100644 drivers/cpuidle/poll_source.c > > diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile > index 26bbc5e74123..994f72d6fe95 100644 > --- a/drivers/cpuidle/Makefile > +++ b/drivers/cpuidle/Makefile > @@ -7,6 +7,7 @@ obj-y += cpuidle.o driver.o governor.o sysfs.o governors/ > obj-$(CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED) += coupled.o > obj-$(CONFIG_DT_IDLE_STATES) += dt_idle_states.o > obj-$(CONFIG_ARCH_HAS_CPU_RELAX) += poll_state.o > +obj-$(CONFIG_ARCH_HAS_CPU_RELAX) += poll_source.o > obj-$(CONFIG_HALTPOLL_CPUIDLE) += cpuidle-haltpoll.o > > ################################################################################## > diff --git a/include/linux/poll_source.h b/include/linux/poll_source.h > new file mode 100644 > index 000000000000..ccfb424e170b > --- /dev/null > +++ b/include/linux/poll_source.h > @@ -0,0 +1,53 @@ > +/* SPDX-License-Identifier: GPL-2.0-or-later */ > +/* > + * poll_source.h - cpuidle busy waiting API > + */ > +#ifndef __LINUX_POLLSOURCE_H__ > +#define __LINUX_POLLSOURCE_H__ > + > +#include > + > +struct poll_source; > + > +struct poll_source_ops { > + void (*start)(struct poll_source *src); > + void (*stop)(struct poll_source *src); > + void (*poll)(struct poll_source *src); > +}; > + > +struct poll_source { > + const struct poll_source_ops *ops; > + struct list_head node; > + int cpu; > +}; > + > +/** > + * poll_source_register - Add a poll_source for a CPU > + */ > +#if defined(CONFIG_CPU_IDLE) && defined(CONFIG_ARCH_HAS_CPU_RELAX) > +int poll_source_register(struct poll_source *src); > +#else > +static inline int poll_source_register(struct poll_source *src) > +{ > + return 0; > +} > +#endif > + > +/** > + * poll_source_unregister - Remove a previously registered poll_source > + */ > +#if defined(CONFIG_CPU_IDLE) && defined(CONFIG_ARCH_HAS_CPU_RELAX) > +int poll_source_unregister(struct poll_source *src); > +#else > +static inline int poll_source_unregister(struct poll_source *src) > +{ > + return 0; > +} > +#endif > + > +/* Used by the cpuidle driver */ > +void poll_source_start(void); > +void poll_source_run_once(void); > +void poll_source_stop(void); > + > +#endif /* __LINUX_POLLSOURCE_H__ */ > diff --git a/drivers/cpuidle/poll_source.c b/drivers/cpuidle/poll_source.c > new file mode 100644 > index 000000000000..46100e5a71e4 > --- /dev/null > +++ b/drivers/cpuidle/poll_source.c > @@ -0,0 +1,99 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > +/* > + * poll_source.c - cpuidle busy waiting API > + */ > + > +#include > +#include > +#include > + > +/* The per-cpu list of registered poll sources */ > +DEFINE_PER_CPU(struct list_head, poll_source_list); > + > +/* Called from idle task with TIF_POLLING_NRFLAG set and irqs enabled */ > +void poll_source_start(void) > +{ > + struct poll_source *src; > + > + list_for_each_entry(src, this_cpu_ptr(&poll_source_list), node) > + src->ops->start(src); > +} > + > +/* Called from idle task with TIF_POLLING_NRFLAG set and irqs enabled */ > +void poll_source_run_once(void) > +{ > + struct poll_source *src; > + > + list_for_each_entry(src, this_cpu_ptr(&poll_source_list), node) > + src->ops->poll(src); > +} > + > +/* Called from idle task with TIF_POLLING_NRFLAG set and irqs enabled */ > +void poll_source_stop(void) > +{ > + struct poll_source *src; > + > + list_for_each_entry(src, this_cpu_ptr(&poll_source_list), node) > + src->ops->stop(src); > +} > + > +static void poll_source_register_this_cpu(void *opaque) > +{ > + struct poll_source *src = opaque; > + > + lockdep_assert_irqs_disabled(); > + > + list_add_tail(&src->node, this_cpu_ptr(&poll_source_list)); > +} > + > +int poll_source_register(struct poll_source *src) > +{ > + if (!list_empty(&src->node)) > + return -EBUSY; > + > + /* > + * There is no race with src->cpu iterating over poll_source_list > + * because smp_call_function_single() just sets TIF_NEED_RESCHED Hum... what about CPU-0 CPU-1 poll_source_start poll_source_register IPI'ing CPU-0 Perhaps a llist can be used? > while (!need_resched()) { > + poll_source_run_once(); Probably want to use static_key's for ->start, ->stop and ->poll?